All of the bad press over the lack of dedicated servers amongst other things may have had the impact some were hoping it would. Far from sales asserting to Infinity Ward that people will take what they're given, the opposite seems to have happened.
Note the very sharp drop in sales - from 5 to 20 in 1 week, whilst 360 and PS3 still sell. Word of mouth has seemingly gotten around, and MW2 is suffering for it.
I wander if this has happened in the US?