I dunno... they probably make a lot of money on selling the hardware and of course don't want to give that up. They see producing a Mac that can run Windows as the best way and I SERIOUSLY doubt they want to produce OSX for the PC as much as we would all love it. Drivers are not a problem if you buy a PC with the same hardware as a Mac has, but skip all the Mac expense and pretty case.
Linux hardly has driver problems anymore... but then the 'easy' distro's do seem to be more unstable than one where you have to work hard at setting it up yourself. Having said that if you run standard stuff they all work well. We have a Linux PC running on a 800MHz Intel PIII with Asus Intel based board that has run almost for 5 years without crashing. Only things like a Fan ceasing up in the PSU, hard disk failing, power-cut etc have made it need a reboot. It's only dodgy video cards and the latest go faster mobo chipsets that make it fall over.
Anyway, like you say maybe if you get the same basic mobo that the mac runs then get a 'hacked' BIOS flash it will all be groovy.