Why do people take it seriously when one ...

For example, with many PS3 game people say teh X360 isn't strong enough, the devs said so... Yet most of the times the devs just say it can't be done(with no reasoning-Heavy rain, MAG), or usually say because of blu-ray-(eg: KZ2, UC2-the dev also says because of the motion blur as well, but lol). Yet games that could not be done previously: GTA4, DMC4, MGS4/raiden(will probably have better graphics than MGS4), also red faction with it's incredible physics(should only be possible on cell:P). At this point don't people see it is fallacy?