In another tidbit from the Activision-Blizzard Analysts day event, Kotaku is reporting that Blizzard announced that the total cost of supporting the World of Warcraft game to date has been $200 million. While the complete details were not released it seems that this number does not include the development costs for the game but simply the cost of keeping servers up, and support personnel staffed.
In any case with more than ten million subscribers and the pending release of Wrath of the Lich King to keep them around, Activision-Blizzard is clearly making a fortune from the king of massively multiplayer games.