Sony does it all the time, they just haven't done it as much recently. I'd say all the publishers do it. Nintendo even did it with RE4 for GameCube. But in all fairness I think the main purpatraitors of buying exclusives has to go in this order.
1.Sony
2.Microsoft
3.Nintendo
Yes Microsoft has done it alittle bit lately but anybody remember Final Fantasy back when Sony signed them up to make FF games exclusively for Sony products. I remember they had to find a way around that to release CrystalChronicles on the GameCube. It was a big issue that Sony had paid Square off. Then theirs all of the exclusives Sony gets on a regular basis for pay offs.Anybody hear about Arkham Asylum? Sony does it far more then even Microsoft and Microsoft is getting really good at it these days.
I think Sony would have purchased the exclusive rights to GTA's DLC if Microsoft hadn't paid so much. I can't remember how much Microsoft paid but I think it was around like 50-mill wasn't it. Sony could develope 3 big budget games for that price it was no longer feasable to buy the exclusive rights.
I think this statement just goes to show you how much Sony and Microsoft rely on third parties to sell their hardware when compaired with first party Nintendo who pretty much doesn't even need or care for exclusives. Nintendo can sell its hardware off first party software alone while Microsoft and Sony have to fight tooth and nail to get each others exclusives!