Almost two years ago, I wrote a piece for the Mac Observer entitled “The Every Other Year iPhone Club.” In it, I explained not only why I was upgrading my original iPhone to the then-new 3GS, but why I hadn’t upgraded to the 3G a year before.

This year, I find myself in a similar situation: I love my iPad, and though I’d love it even more if it were faster and had two cameras, those new features are not enough to warrant buying a whole new device. Projecting a while further into the future, I’d be surprised if the iPad 3 had enough new bells and whistles to make me move from an iPad 2. But going from an iPad 1 to an iPad 3? I suspect that’s going to be a no-brainer.

And it seems like I’m not alone. Early reports say that up to 70% of iPad 2 purchasers were first-time buyers. That’s also great news for Apple, because it means they’re expanding their installed base — making it even harder for competitors to catch up, if and when they start actually shipping.

The phrase “evolutionary not revolutionary” has become cliche in describing the iPad 2, but it’s accurate. It’s also a smart strategy. By focusing on moderate but incremental improvements, Apple will continue to grow its customer base, while minimizing the backlash from its installed base (“Whaddaya mean I can have all these great new features — I just bought this thing?!”)

Apple’s resurgence and continued success has been built on the idea of introducing a revolutionary concept (iMac, iPod, iPhone, iPad — even the MacBook Air) in a basic — almost vanilla configuration — and then gradually to add significant features to it.

That steady, sustainable growth strategy is a concept that seems so simple and so obvious, yet it’s one that amazingly few others in the tech world seem to grasp.

Now: back to saving up for that iPad 3.