soundwave has a point..it is a risk that they'd marginalise the series if they put it on a less successful console exclusively. If Take2 had to bet right now, I think their money would be on Sony. The most popular systems make kings out of certain games..if Sony maintained a significant userbase advantage over their competitors, and GTA wasn't on it, heaven forbid something like The Getaway could eclipse it as a must-have series

GTA, would not have become the series it is (commercially) if it hadn't been on Playstation. Is Take2 willing to bet Sony won't hold a significant lead next gen? That should answer the question, at least as far as timed exclusivity versus full exclusivity is concerned.
Izzy is putting me off the scent a little, but I wouldn't be at all surprised to see GTA timed exclusive on X360.