In the Q2 2011 earnings call, when Cataclysm's subscriber number dipped to 11.4 million after the post-release bounce, Mike Morhaime referred to that figure as a "return to the pre-Cataclysm subscriber numbers" - meaning that Wrath's end-period subs were also 11.4 million. Blizzard simply timed their releases to present a more rosy picture of events to shareholders so that the sub loss between September and December 2010 during the end of the year of Icecrown was made invisible by the bump from Cataclysm's December 7th release.
Do you get it now?