Now, the first issue we'd have with these numbers is the situation in China -- Hunter doesn't mention it at all, and in fact his graph (from comScore) doesn't have any dips at all in it, even though the game, and presumably its millions of players, went offline over there earlier this year. That right there throws a wrench into all of these estimations -- it's very likely comScore's information is just plain wrong.
But then again, Ghostcrawler himself told us recently that subscriber numbers are still growing, and the last "official" numbers we heard were from nearly a year ago, so it's not beyond the realm of possibility that Blizzard is close to 13 million, if not there yet (many Chinese players, we've also heard, could have transferred over to Taiwanese servers. Of course, if this is true, and WoW is bigger than ever, odds are that we'll hear it officially from Blizzard soon -- they're not shy about sharing information about the game, especially when it's good news for them. If there really are over 13 million computers in the world running World of Warcraft, don't be suprised to see that information in an official press release sooner rather than later.