The new MacBook Air announced at yesterday’s Macworld keynote doesn’t disappoint; it’s pretty much the laptop I’ve wanted ever since I stupidly broke my 12” Powerbook trying to replace the hard drive. All things remaining the same, I’d buy it simply for the difference in weight, a full two pounds less than a MacBook. As someone who’s put a lot of miles on his kicks with a laptop bag on his shoulder, that would make a world of difference.

What’s interesting though, is what the MacBook Air isn’t: it’s not simply a sexier MacBook Pro on Jenny Craig, it’s a different class of machine. John Gruber rightly points out that it’s clearly designed as a secondary machine for people who do their heavy lifting on a desktop. Without another machine standing by at home or the office, only a select group of geeks could really get by without an optical drive, not to mention the diminished overall specs of the MacBook Air may not please a power user without reinforcements (a.k.a., the folks willing to spend upwards of $2000 on a laptop).

What Apple seems to be increasingly good at is designing machines with a specific purpose in mind. Rather than differentiating their products on matters of style or incremental horsepower like so many PC manufacturers, they make you look at their stuff and say, “I want one of those, and I want to use it for this.” In the case of the MacBook Air, it’s made for travelers, commuters, and other wandering souls who want a slim machine for checking email, web browsing, writing, and maybe some lightweight coding while they’re away from the mothership. For the people who want to use a laptop as more of a primary machine, there’s an obvious choice in the clearly differentiated MacBook Pros, or even MacBooks.

The same goes for the Apple TV, which I was glad to see get a new lease on life. I love mine, and I’m happy that it won’t be relegated to the ghetto of second-hand eBay trading and parts hacking, at least for another year. Apple could have chosen to discontinue it and market, say, the Mini + Front Row as a multimedia computer suitable for attaching to a home entertainment system, a la Windows Media Center, but instead it chose to put its money a device that is specifically designed for doing so, not just a general purpose computer with a few remote control-friendly screens pasted on front.

To return to the same note I always manage to hit here, the key is simplicity. Apple makes it easy for people to simplify their computing environment—“I use my iMac for this, I use my iPhone for this, I use my Apple TV for this,” etc, etc. I made a promise to myself that I’d stop buying computer gear without a specific purpose in mind for it, and I’m not currently in the laptop market because I rarely stray from my home office. But damn if they aren’t making me rack my brain for a reason to need one again.