They design their games for the PC first, something I appreciate greatly.
It seems that they port to the XBOX360 because it is similar to PC and easy to port the code over.
PS3, however, is harder to program for and much more different than the PC than the XBOX360 is. People say they are laze, but it is a cost vs. benefit consideration they are taking into account. Either they see to cost for porting their games to the PS3 is more than their projected revinue from it or they have all their work force working on more profitable projects.