It's still a tremendous amount of sales and IW must be pissed that the brand they created continues to do so well without them.
Why? They are likely to work on the next one (they usually do every other one). Most consumers don't care about who makes the game, they care more about the COD name than the studio making it.
I care, because the Treyarch games are (in my opinion) markedly superior to the COD games made by Infinity Ward. Treyarch makes an effort to crack down on boosters and hackers in the game, but Infinity Ward doesn't even give a damn. Infinity Ward introduced tactical insertions which cheating punks exploited all to hell and then they sat on their ass and never did anything about it. Well, Treyarch did something about it in Black Ops. You might not think it matters, but if you've ever played Free For All in MW2 and suddenly had a nuke called in on you by some 12 year old punk letting another 12 year old punk kill him over and over 25 times in a row in order to get that nuke you might understand.
Plus the Treyarch COD games are the ones which have zombies, which is a major plus for me. And I also like that Treyarch supports Nintendo 100% by releasing Black Ops for the Wii on the same day as the other systems. Infinity Ward never gave a damn about Nintendo, and so MW2 never came to the Wii. So if Infinity Ward is pissed and unhappy, then I say good, because they are a bunch of assholes as far as I'm concerned. They can take their booster friendly Nintendo neglecting crappy COD games and shove them where the sun don't shine.