What makes the iPad so new and different, of course, is that instead of you having to find a bootleg copy of Apple’s OS X operating system and install it illegally on an existing netbook or tablet PC, now you get to have a real Mac system pre-installed on a super-lightweight device that’s fully capable of running it.

Except, of course, you won’t. The iPad—contrary to the way most people thought about it—is not a tablet computer running the Apple operating system. It’s more like a very big iPhone, running the iPhone operating system. As Jobs explained at the unveiling Wednesday afternoon, netbooks don’t do computing as well as computers, so why make one? Instead, the iPad means to fill the middle space between a phone and a laptop, and to be really good at that. Like a really big iPod Touch.

While this certainly makes it useful in the way that a Kindle (only with an eye-straining backlit screen) or a big PDA (but really big) might be useful, it also encourages us to do more of our daily computing in the walled gardens of Apple’s iTunes and Apps stores.

For years, now, Apple has been struggling to make its popular retail shopping applications profitable. Just last week, in fact, when releasing the company’s quarterly reports, Apple CFO Peter Oppenheimer admitted, “Regarding the App Store and the iTunes Store, we’re running those a bit over break-even, and that hasn’t changed. We’re very excited to be providing our developers with just a fabulous opportunity, and we think that’s helping us a lot with the iPhone and the iPod touch platforms.”

So maybe they’re not really struggling so much, after all.

In other words, these programs and online stores are really loss leaders for the hardware people have to buy in order to use them. And now that there are so many cool apps and publications available through the app store, Apple has created the ultimate device for enjoying them: an iPhone big enough to read a book or watch a movie on.

Most importantly though, like the iPhone, the iPad will get its content from iTunes and the App Store—places where people actually have to pay for the stuff they download. This is welcome news to publishers of all types of media, who have been decimated by the Internet’s “cult of the free.”

But if history is any guide, joining up with Apple doesn’t really generate the kind of revenue content providers might expect. Recording companies featured on iTunes lose money as their albums are sliced into singles that cost a whole lot less.

And while Apple might wish the best for its content partners, its business model is about selling hardware. Keeping its Mac operating system exclusive to Mac hardware is the main reason the computers sell so well—and at such a premium. Likewise, the songs in iTunes make the iPod worth owning, the preponderance of great software in the Apps Store makes the iPhone worth its price, and—if they succeed—the bounty of content in new online venues will make the iPad the next device for which to shell out good money.

It’s an interesting model, almost exactly the opposite of Google’s, which is what makes Apple so interesting. Google makes its money by giving everything away: software, storage, email, and content that can work on the cheapest hardware, made by pretty much anyone. Like free television, all of this gets paid for with advertising dollars. Apple is more like HBO in this respect, offering premium content that’s a lot easier to pay for than descramble.

So Apple continues to retool itself and its devices to this more closed, proprietary universe of content and applications that can only be purchased and installed through various online Apple stores. I’m not saying that this is necessarily bad for everyone, particularly not for those lucky enough to write a popular app or consumers who like things to work easily. And it does create some alternative to a world with nothing to sell except Google ads. But all this iStuff might end up doing to the traditional Macintosh what the Mac did back in the 1980s to the venerable Apple II—that is, replace it.

The Mac system already bends over backwards to accommodate the needs of its iPhone system brethren. Apple’s mail and storage servers were on the fritz for months as Mac turned into the iPhone-friendly MobileMe. And like almost every Mac user I know, I am sick and tired of my iTunes application trying to update itself what seems like every couple of days, along with Apple’s ever-changing, always-more-restrictive approach to content management and licensing. It feels as if ever since the iPhone was released, the Macintosh computer has become just another leverage point in this other operating system’s marketing plan.

In the new 30-million-iPhones-strong Apple universe, OS X is old school. It’s a relatively open system, onto which I can install any program, get to any content, and even change how it works. I’m not obligated to go through Apple. That’s why instead of bringing the Mac OS down to its new devices, Apple is bringing the closed iPhone system up.

As Apple continues to release new styles of netbooks, laptops, and even desktops with untold movie-watching and game-playing capabilities, I wouldn’t be surprised to see the iPhone operating system running on them—and the Macintosh eventually becoming a thing of the past.