Rumors have been flying that it is because of the PS3 that the delay occurred. But on the plus side, there is also a HUGE rumor from a reliable source that Sony is making a move to acquire majority control of Rockstar, which means that GTA would be an exclusive Sony franchise once again...

I would definitely think that instead of pissing off Microsoft by having the versions of the game released when they are ready, R* is showing a bit of favoritism towards Sony by keeping GTA under lock and key until the PS3 version is ready.

The good news I've heard? Starting next year, EA is building all of their next-gen titles based off the PS3, rather than porting from the X-Box 360 and having delays for PS3 versions, which will be a nice change.