The reason for the stability in the Apple OS is due to the limited hardware options.
I think this hits the nail on the head really. The whole point of macs has always been that the hardware and OS are designed and built by the same company, thus avoiding so many of the variable that exist in the PC world, that can give rise to unexpected problems.
I'd also note that within that PC world, the way most of us eventually attain comparable stability to the mac is by taking a similar route: ie narrowing the options. We research which chipsets, audio hardware etc are known to work well together, and focus on those. We don't just install any old free game and plug any old cheap device into our computers while we're in the middle of an important audio project.
So using a hacked OSX on a PC it was never designed for would seem a very odd thing to want to do, as it would satisfy neither of these ways of doing things. Apart from anything else, if you've got enough patience to want to bugger about with something like that, then it's really not that hard to set up a comparatively stable PC using WinXP.