Yes they make a ton of money off of the game, but how much do you think they pay each month out of that money for the games bandwidth, server maintenance, and employees who continue to work on new content and fix/balance current content? Yes they still make a healthy profit, but they also shell out quite a bit each month to ensure that those 10+ million subscribers have a smooth and reliable experience.

Of course they do, there will always be overhead. Remember this is Blizzard though. They've had more then a few hit titles which has most likely landed them a few good connections in the world. There is no way of us knowing what they have to account for each month or year, but I'm betting it's no where near the roughly 2 billion dollars they pull in each year from subscriptions alone. That's not even accounting for merchandise or other misc income.

Barely a third of that number pay 15 dollars a month, Blizzard has already said a big if not half of the player population is from Asia who can use prepaid time cards that count down on a credit system

I wish we had something like that in the US but that would kill profits since a large portion of the wow community does not play a lot.

Well, those in china pay like 0.06 $ per hour for WoW, and they only pay for the time they actually play. And since those are a big slice of the 10 million playerbase, the actual income is way lower for Blizzard.

Nevertheless, there's still a 40% profit from WoW (at least that's the figure I remember...)