I think most of it is out of principle tbh, not necessarily the price.
I mean, If right now they brought out the half life series and I knew what it was, i would happily pay the equivilent in £ for $60 worth because it is such an epic game. I think I would consider the same for CoD4, but when they have dicked about with MW2 and made the online crap for PC and very samey to CoD4, only with 1 extra game mode and a bit of extra customisability, it doesn't seem worth it. IW had 1 (ONE) good game and now they think they can sit tehre charging more than everyone, because they had ONE good game.
What I love most about it is that on steam, whenever a new game comes out for preorder, straight away it always shoots to the top of the preorder list...
MW2, even though it is cheaper than buying in store, hasn't broken 3rd spot