Chalk it up to the narcissism of small differences. Apple and Microsoft look more like each other than either do any other tech company. They’re both software-focused firms in their mid-thirties with global reach in multiple markets. Both make a lot of hardware (although Apple makes more). Both of their CEOs are stuck with the impossible job of following founder-prophets who saw the future of personal computing through and beyond the traditional PC. And both are obsessed with playing up mild differences in those visions by fixating on slight variations in language.

Hence today’s rhetorical diversion from Microsoft COO Kevin Turner, reported earlier by The Verge’s Tom Warren, pitting Microsoft vs. Apple, “PC Plus” vs. “Post-PC.”

Turner’s slide, titled “In Our View, Apple Has It Wrong!”, points to quotes from Steve Jobs in 2010 and Tim Cook in 2012 emphasizing the differences between tablet computers and traditional PCs, and announcing the beginning of the “Post-PC era” with the introduction of the iPad. Turner then introduces Microsoft’s preferred phrase, “PC Plus.” In fact, Jobs was publicly using the phrase “post-PC” in discussions of the iPhone and iPod at least as early as 2007. Meanwhile, “PC Plus” is even older; as Tom notes, it was used by Bill Gates in a Newsweek op-ed all the way back in 1999, in more or less the same way that Turner and Microsoft using it today.

What’s more, when you examine them, these two frames of “PC Plus” and “Post-PC” are virtually identical. Both are describing a world where increasing mobility and cloud storage blur the distinctions between software and data on different devices. There are some differences in development strategy and user interfaces. But mostly, Microsoft’s rhetoric emphasizes innovation moving outward from the PC to Xbox or phone, and Apple’s rhetoric emphasizes innovation moving from mobile devices like the iPhone and iPad “back to the Mac.”

Structurally, though, the differences aren’t really that big. It’s two highly competitive companies beating their chests, asserting their dominant position over the evolving personal computing landscape, and announcing, “we’re in charge here.”

Here’s what Gates said in 1999 about the coming “PC Plus” landscape:

For most people at home and at work, the PC will remain the primary computing tool; you’ll still want a big screen and a keyboard to balance your investment portfolio, write a letter to Aunt Agnes, view complex Web pages, and you’ll need plenty of local processing power for graphics, games and so on. But the PC will also work in tandem with other cool devices. You’ll be able to share your data — files, schedule, calendar, e-mail, address book, etc. — across different machines; you won’t have to think about it; it will be automatic. If you want to find the best price for a new car — and check out your budget to see if you can afford it — you’ll be able to do that at the dealership, on the device you have with you. Wherever you are, whatever you want to do, you’ll have all the information you need.

Now, here’s what Steve Jobs said in 2007 — as it happens, sitting right next to Bill Gates (and across from AllThingsD’s Walt Mossberg and Kara Swisher) — when Jobs first began publicly throwing around the phrase “post-PC”:

I think the PC is going to continue. This general purpose device is going to continue to be with us and morph with us, whether it’s a tablet or a notebook or, you know, a big curved desktop that you have at your house or whatever it might be. So I think that’ll be something that most people have, at least in this society. In others, maybe not, but certainly in this one.

But then there’s an explosion that’s starting to happen in what you call post-PC devices, right? You can call the iPod one of them… There’s just a category of devices that aren’t as general purpose, that are really more focused on specific functions, whether they’re phones or iPods or Zunes or what have you. And I think that category of devices is going to continue to be very innovative and we’re going to see lots of them.

So clearly, neither Jobs nor Gates restricted the idea of “the PC” to any one operating system or form factor. And both emphatically insisted that the PC would continue to both evolve and endure, surrounded by a broad, versatile class of computing devices extending the definition of personal computing.

In 2007, both Jobs and Gates were also really, really bullish on tablets. Astonishingly so, given the history of tablets up to that point. In fact, there’s a wry moment in that joint interview where Mossberg notes that the tablet form factor “has not necessarily stormed the world yet.” Gates’ reply (“This is like Windows 1992, I think. That is, I’m unrepentant on my belief” in tablets) suggests he thinks that the tablet is about three years from mainstream acceptance. I doubt Gates believed Apple would be the company to make that happen in 2010. Then again, few people at Apple in 1992 probably fully realized what Windows 95 would do to mainstream acceptance of GUI on PCs and further marginalize the Mac.

Gates, though, precisely predicts what he thinks a future tablet PC will look like, and it’s pretty much equal parts a third-generation iPad and a Microsoft Surface running Windows RT (flanked by a smartphone, an Xbox 360, and some things we’ve seen coming out of Microsoft Research):

[In five years], I don’t think you’ll have one device. I think you’ll have a full-screen device that you can carry around and you’ll do dramatically more reading off of that… I believe in the tablet form factor. I think you’ll have voice. I think you’ll have ink. You’ll have some way of having a hardware keyboard and some settings for that.

And then you’ll have the device that fits in your pocket, which the whole notion of how much function should you combine in there, you know, there’s navigation computers, there’s media, there’s phone. Technology is letting us put more things in there, but then again, you really want to tune it so people know what they expect. So there’s quite a bit of experimentation in that pocket-size device. But I think those are natural form factors and that we’ll have the evolution of the portable machine. And the evolution of the phone will both be extremely high volume, complementary — that is, if you own one, you’re more likely to own the other…

[At] home, you’ll have your living room, which is your 10-foot experience, and that’s connected up to the Internet and there you’ll have gaming and entertainment and there’s a lot of experimentation in terms of what content looks like in that world. And then in your den, you’ll have something a lot like you have at your desk at work. You know, the view is that every horizontal and vertical surface will have a projector so you can put information, you know, your desk can be a surface that you can sit and manipulate things.

So even here, Gates is backing away from the idea that any one of these devices is the core or hub around which all the others orbit. In fact, his vision of personal computing is much more radically decentered than the laptop plus smartphone scheme Jobs is publicly endorsing. For Jobs, “post-PC” is first and foremost a device category, a way of describing an emerging class of “computers in another form factor,” the coupes and sedans beginning to distinguish themselves from a universe of trucks.

It’s really not until you get to iCloud in 2011 that Jobs starts to use “post-PC” to describe what he described in 2007 as the evolution of the PC:

About 10 years ago, we had one of our most important insights. We thought the PC would be the hub for your digital life. What did that mean? Where you put your photos, your video, your music. You were going to acquire it, and sync it to the Mac, and everything would work fine.

And it did, for the better part of ten years, but it’s broken down in the last few years… Why? Because all your devices have changed. They now all have music; they now all have photos… and keeping these devices in sync is driving us crazy!

We’ve got a great solution for this problem. We think this solution is our next big insight. We’re going to demote the PC and the Mac to just be a device. Just like an iPhone, or an iPad, or an iPod Touch. We’re going to move the digital hub, the center of your digital life, into the cloud.

That’s all “post-PC” means: a move from manual wired to automatic wireless connections between devices, where syncing, computing, and notifications can all be done through communication between client apps and backend services. It’s the end of the PC’s hegemony over the computing universe, not its death and decay. That’s what Jobs meant by it, and what Tim Cook means by it. Fundamentally, it means exactly the same thing as Bill Gates and Steve Ballmer and everyone else at Microsoft has always meant by “PC Plus.”

Now, to be fair, the two companies do have genuine differences, but mostly over a rapidly diminishing set of choices when it comes to what could arguably be called post-PC devices. Here are most of them:

Seriously; that’s about it.

Are we really going to pretend that one of these companies trying to link multiple devices to the cloud is indisputably right and the other is incorrigibly wrong?

After all, the Amazons, Googles, and Facebooks, web companies still in their adolescence, are nearly as similar to each other as Apple and Microsoft. Devices for Amazon or Google become pure appliances, throughways to user data, media consumption, and purchase intent. You make the hardware and media as inexpensive as possible and make up the balance through what you can learn about your users and how they use your services.

The more that these companies learn that they can gain by keeping users on platforms that they control, the more skeptical their traditional PC partners become of their services.

That’s the distinction that matters today: not sibling rivalry, but generational conflict.