Even if it was true, and those numbers are in no way realistic,

which numbers

it would still be a bad business decision,because of 2 main reasons:

1) Even if only 30% of the sales came from xbox and pc, we are still talking about MILLIONS.Rocksatr wouldnt just throw it all away just for some exclusivity deal that will do more harm than good(and that includes the marketing costs that supposedly sony would cover, which again wouldnt happen.They wouldnt at least cover it 100%, because it is alot of money to spend in one game that is not even owned by them.)

30% of the sales would still come after 1 year when Timed exlcusivty runs out

 40% GTA 5 sales came in its second year so the gap would easily be covered

SONY would add not cover marketing cost,ROCKSTAR itself spent $200million on marketing for GTA5 and SONY spent an additional on its own without contract $50-100 for GTA5,its would easily hype it much much more

there would be no hard done atall,it would acutally hype the game even more.for GTA they would easily cover marketing costs when it wins them generation by 1 game itself and the sort of console sales and brand power it will bring.that part it so obvious.

2)That would piss off fans, and that is the worst mistake here.Fans are the best marketing a game could ever get, and by doing this move they would only hurt the brand.

So no, this is not happening.

it wouldn't piss off many fans as alot f PS4 users are 360 user and for a GTA game it doesn't even matter.fans change teams for big games like GTA and CALL OF DUTY with even a tears,the game is that big and fans getting pissed off and whining is pretty common in gaming.it wuldn't change anything.

it doesn't matter. The game has the potential to sell at least 5-10m range on xbox.  The franchise cost too much to make nowadays to make it only exclusive.