Why would they (R*) Want to keep GTA exclusive on PS2? When clearly the more powerful and better graphics system is waiting? Oh thats cuz Sony paid them to...Same with Agent.
http://playstation.joystiq.com/2008/05/30/kaz-hirai-sony-can-re-evaluate-paying-for-ps3-exclusives/
Now to quote it.."A long time ago, Jack Tretton mentioned that Sony will not pay for PS3 exclusivity in this generation of games" Which means Sony did indeed pay R* and other game companys.
Even one from VG chartz
http://vgchartz.com/forum/thread.php?id=65741
Another http://www.joystiq.com/2009/04/21/sony-pub-fund-paying-off-for-psn-exclusive-devs/
