Just a note on sales, marketing, Call of Duty, and Activision.
My basketball coach in highschool gave the team a lesson during our first practice senior year. We had split up into 2 groups, and were playing a short skirmish game. My team had possesion, and we ran a smoothly exicuted pick-and-roll play, and scored.
Our next possesion, our point guard decided not to be predictable and called for a different play. Our coach blew the whistle and stopped the game.
"Why did you use a different play?" He asked. "The pick and roll worked the first time, right?".
Our point guard responded "I thought they might be ready for it this time". Our coach smiled and asked "If a play works, how many times to you repeat it before you switch to a different play?".
Our entire team started throwing out random gueses, but we had clearly missed the point.
"You use the same play as long as it works. If you run that pick and roll, and you score, then do it again and again and again until you don't score. Why change your play if you are scoring with it?"
That is EXACTLY the approach Activision takes in general, and specifically with Call of Duty. They don't give a crap about game quality or driving the medium forward. They care about making money. Or perhaps I should say, the way they judge the quality of a game is by looking at how much money it makes.
If Call of Duty keeps selling more than any other game, then Activision will not allow it to change. If Modern Warfare 3 doesn't break all kinds of sales records, then we might see things get shaken up a bit. But as things are going right now, Activision doesn't need to change their play... they are scoring every time.