It would probably be very possible to port OS X to x86 hardware, if you were apple.
But they aren't going to do that, they make money by selling hardware, not by selling software.
Like the iTunes online system. They don't care if they make money by selling songs on-line, because they make the profit by selling the iPods to people so that they can play the music away from there computers. Any profit coming from iTunes itself is just a nice bonus.
Designing a modern OS is very expensive. Only one company pulls off just making profit on OSes alone, and that's Microsoft of course. And that's just because they have the economy of scale behind them. So if they sell at a loss for some versions and discounts and only make 10-20 off of each Windows copy sold thru normal retail avenues then they still make gobs and gobs of cash overall.(that and MS office are Microsoft's only profitable software products)
I think that if apple wanted to make a profit off of x86 from selling software alone. (either up or become another Dell/Gateway/HP cutrate low-profit margin seller...) Each copy would have to cost in the order of 500-1000 dollars apeice.
After all, look at comparable software of similar complexity. Like 3d-max or Photoshop are two that are familar for most people. Very pricey. Is a OS any simplier or less technical to manage and develop for?
(Someone could probably steal the source code and port it over easily enough, but who in their right mind would want to devote months of their life to a stolen product that is completely unsupported and probably unusable by the vast majority of any body who would care in the first place?)