To be honest, I think Apple is almost betting that personal computers will be obsolete by then. A lot of the software updates recently, especially for iTunes, Quicktime, and Safari, have been geared toward making the desktop experience more similar to the iPhone experience. Apple hasn't been looking to develop games for the iMac recently, but the iPhone is set to take on the Sony PSP and Nintendo DS as the portable gaming platform of choice. It all points in one direction - away from the home/office, where what we know as OSX runs.
Of course the iPhone is running a stripped-down version of OSX, so there's no reason not to develop them side by side - for now.
There are hardware checks on OSX, but I don't know what they look for. Mostly to make sure its a Mac, and that the video card is supported, I guess. I've heard of Leopard running on G3s, so it can't be that draconian.