The 11 million figure has been consistent since before
Wrath of the Lich King's release.
Here's a press release from Blizzard's site.
http://us.blizzard.com/en-us/company...es.html?081028
Unlike the release of
The Burning Crusade, there was no spike in the amount of active subscriptions.
The good news is that with
Cataclysm in the near future, bringing with it an overhaul of the traditional zones and a portion of the 1 - 60 leveling process, the subscriber base will most likely surpass the 11 million hump.