Unfortunately, Activision are run by a bunch of greedy idiots. No more WW2 games need to be made featuring the word "duty" , "call", "medal" or "heroes".
Halo 3 has such huge sales because it's a huge IP. COD doesn't have that advantage in the fact that COD3 sucked, and while COD2 on X360 was great, it was a launch game (which did awesomely I might add).
COD4 should wind up between 6-7m on the X360 alone - a huge achievement for the game.
Back from the dead, I'm afraid.