The game is still coming to Xbox 360 and PS3. Microsoft obviously handed a big bag of cash to Rockstar to get the game exclusive, which Rockstar denied but took some money and let the game have a simultanious release on the 360 and PS3. Mainly because Rockstar knows most of the GTA fanbase are PS2 owners and that there likely to buy a PS3. That may not be true now but they didnt know back then.

If the PS3 doesnt gather steam Microsoft will eventually have stolen every worthwhile brand Sony has. Sony can put up a fight money wise ( I mean, there still Sony after all ) but with them losing so much money with the PS3 they will have less money to give away soon and Microsoft will probably have more. Microsoft are unfair competition if you ask me, but hey, thats why I bought both consoles.