Everyone knows that it will hit the PS3, Microsoft never said in any of their press conferences that the game is exclusive (while they were signing and dancing about Infinite undiscovery exclusivity and last remnant timed exclusivity),, my guess is that it wil be announced as soon as the 360 one is released.
but in this post E3 Megaton world, u might never know for sure, it might stay exclusive for good! :(