It's a good version of the game, and I commend them for that, but Call of Duty has ecosystems of millions of players on other consoles. In this case, even though it's the best version of the game, it would take a lot to get people to leave them--they'd need to find a way to get people to switch over en masse, or else it wouldn't work at all. This isn't necessarily representative of what all third parties can expect.
Although, I suppose I don't have much of an answer regarding the sales of games like Assassin's Creed.