Going by the fact that they don't use Msaa on 360 because they don't think its worth the trouble to implement a engine feature that could only be used in a single platform, why would they do that? I mean, on Pc there's no need and on Ps3 they already have the code implemented for a nice method for solving this issue, and most likely ran like a charm on their game...
If Ms want developers to use effective anti aliasing techniques, it should at least provide implementation examples on the sdk for people to use.
They also said that developing for the PS3 was a waste of resources because you gained nothing that could benefit other platforms. In other words, "make it worth our while ."
Money is a hell of a drug...