This, ultimately, makes a lot of sense:

This is significant because it means that Apple has now committed to Windows-based performance testing, and it will influence industry-standard testing methodologies going forward, possibly including Mac OS X testing. We speculate that Apple will now develop Windows drivers for Intel Macs like the iMac, Mac mini and MacBook Pro with Intel Core Duo processors. You will probably still need to buy your own copy of Windows XP (or Vista), but this is exciting stuff.

So to make OS X run on generic hardware is illegal, but running Windows on Mac hardware ain't, and is, in fact, even encouraged? I hate to reference Joel's tipping point blog again, but I will (well, have). Now there's really no reason not to buy a Mac when you go in for your next Windows box upgrade other than price, and even that's somewhat debatable if you're into paying for stylish computers. While you're there, it sounds like Apple is convinced that if you use Windows from within OS X, you'll find yourself sticking around. Sounds like a good bet to me.