"It's possible GTA4 PS3 went with the blur because a blur upscale post process pass is much faster than using any form of hardware msaa on PS3. You can do an upscale in ~0.5ms, compared to potentially many milliseconds for msaa. Remember that with msaa, the more stuff you draw the more expensive it becomes. A post process upscale on the other hand is a fixed performance cost regardless of what's going on on screen. GTA4 draws far more stuff that just about any game out there, far more than your typical shooter game, so msaa on GTA4 was probably very expensive on PS3.
Also, a post process upscale will require less memory than msaa will. All games have post process passes, and the upscale step can be fit into that framework with no extra memory required. Given the scope of GTA4, it's possible that they couldn't afford the extra memory hit for any form of msaa on PS3.
Combine the two, both a performance and memory hit, and you can see why they may have chosen to not use any msaa on GTA4 PS3 and instead go with a blur filter. The reason they went with msaa on the 360 version isn't because they are all dumb PS3 programmers at Rockstar that want Sony to fail. They have some serious talent there, they contribute to many of the graphics books that we all read. Instead it's likely because there is no memory hit for using msaa on 360, and the performance hit on 360 is relatively minimal as well.
Finally, you can't compare Killzone2 to GTA4. Those games have totally different hardware demands, it's impossible to compare the two. Open world games like GTA4 are perhaps the toughest most hardware demanding style of games out there to implement."
Source Joker454 (Same as the one 2 posts up) http://forum.beyond3d.com/showpost.php?p=1234947&postcount=958
Tease.
