Well there still is the issue with Achievements being added on the 360 and having to cost money. So in order for it to be free, it would have to have no Achievements...
Riddle me this: If for it to be free, it could not have achievements. Then why did the free co-op DLC for Red Dead Redemption have achievements?
It's because Bethesda wants to try and recoup some of it's losses on this game.