Vivendi (owners of Blizzard) made a massive $1.5 billion in 2007, a great deal of it coming from the Burning Crusade.

We know for sure: it's actually around $1.2 billion (which is up 58% from 2006). Now, you can probably see that that's only $500 million short of the estimate that we were trying to prove was wrong, but don't forget that the $1.2 billion isn't just subscription fees-- it includes all those sales of Burning Crusade last year at full release price. What Blizzard earns from subscription fees is just part of that total.