WotLK will only sell 5 million copies?

Gamasutra/WoWinsider seems to think so. Personally I think that is levels of magnitude too low with over 11 million people currently playing WoW. 5 million copies is less than half of those playing, and there is simply no way less than half are going to want to play WotLK. Not only do I see the vast majority of players sticking around and loading up the expanions, but I also see thousands of new players coming into WoW with its introduction. And when I say the vast majority, I'm saying I believe something on the order of 80-90% of all currently players right now.