What's also remarkable is the longevity of the game. Most successful games peak early and then fade. Not WoW -- it's been a rolling hit since it launched in 2004. WoW grabbed the best-selling PC game title in 2005 and 2006 and The Burning Crusade expansion pack was the bestselling PC game of 2007 in North America and Europe. Burning Crusade also holds the record for fastest selling PC game of all time, moving 2.4 million copies in 24 hours and 3.5 million in its first month of availability.

The next expansion pack for the game, Wrath of the Lich King, will be released November 23 and should set similar sales records.

Colin Sebastian, analyst with Lazard Capital Markets wrote in a research note to clients in mid-October that he expected "a net addition of ~1M new subscribers" to the game over the next 12 months, due in part to the Wrath expansion pack and ongoing growth of World of Warcraft in China. In the note, Sebastian wrote that WoW was already approaching 11 million paying users, so he anticipates growth to 12 million over the next year.

Worth noting is the unique way that Blizzard counts WoW "subscribers." In Asia, rather than paying a monthly subscriber fee, users typically buy prepaid cards with game time on them at Internet cafes. Blizzard counts subscribers by combining the number of non-expired prepaid cards as well as users accessing the game from cafes in the last 30 days.