Think about it

If you buy OS X and hack to run on a homegrown box, Apple doesn't really care. You bought OS X for $129 (or $29 this time around, yay!), which they wouldn't have gotten otherwise. You probably got it to tinker around with, test drive, poke around here and there ... remember, Woz and Jobs started off selling to hobbyists. They're cool with it, but don't, of course, expect much help from customer support or a genius bar.

Now, if you do that and start reselling the computers, then they got issues. Their cost of doing business will escalate as people call in for support. Their reputation drops as the quality is iffy, and Apple has built their reputation for quality goods; it's a large part of what keeps them profitable even in this consumer market. And the people you're selling to are far more likely to be people who would buy a Mac, thus cutting under their profit. And just how much are you returning to Apple for each copy of OS X sold?

Different cases. One is being a hobbyist, the other is using the OS in a way that is against the EULA and undermines Apple's business.(And this from a pro-business libertarian, I'll have you know.)