Microsoft payed Bethesda to release it first on Xbox. It is not as if Bethesda favors the Xbox by any means.
And anyway, what do you expect when you bought a blue ray player as your primary gaming console?
It's good that MGS:Rising is coming for PC.
Charge you a trivial amount in "punitive damages," the kind of amount Beth wouldn't bat an eye at. The odds of a serious judgement in MS' favor are not good. Were this a launch title or MS did a ton of advertising it would be a different story. Consoles are very release-day oriented as a market. The big sales have already been made.
But PS3 gamers always get the worse end of the stick when it comes to multi-plat games, simply because the Xbox 360 is more like a PC and hence easier to develop games on than the PS3. This is why I have an above-average gaming PC and an Xbox 360 - because as far as I can see, there are NO benefits to the PS3 over the 360. I'm not trying to start a flame war, I'm sure it's mostly down to preference rather than anything in particular for most people, but as I can see, the PS3 is the worst of the proper consoles with PC, obviously, the best for gaming on the whole.