It has been announced by Rockstar Games that GTA 5 will be coming in 2010 and exclusively on PS3.They also said that it will be more like San Andreas,very big and not like GTA 4.They also said that they first had decided to make GTA 4 very big like its own San Andreas but had to cut the game down because there weren't enough PS3'S sold at that time and they cut down the game to make it fit on the XBOX 360.Below is a link stating that :
http://www.video-game-forums.com/general-gaming-cross-platform/62100-gta5-ps3-exclusive.html
I read the magazine and then did a google search and found out articles on IGN and Gamespot about it.