During the call, CEO of Blizzard Entertainment Mike Morhaime pointed out that World of Warcraft had fallen again to pre-Cataclysm subscriber levels -- 11.4 million subscribers at the end of March, down from its peak of 12 million. Subscriber levels do not decline linearly, he pointed out, stating that they fluctuate based on how quickly players consume and complete content. Players are consuming Cataclysm's content faster than any expansion before it, so subscriber levels started to drop off more quickly than they have previously.
11.4 million subscribers still puts World of Warcraft quite far above and beyond any of its competition, and it should be noted that the numbers stated in the call came during a slow point in the expansion -- Cataclysm launched in early December, putting the end of March a good four months out. You can only expect players to consume the same content for so long, and four months is a pretty long time. If this were a single-player game and not an MMO, no developer could reasonably expect a player to consume the same content for four months. That's one-third of a year with no additions to the game, and we've only just received a content patch at the end of April. It's actually surprising to me personally that four months is faster than previous expansions.
The month of March may also have just been a bad month to poll, as competition such as RIFT launched that month. Even if the majority of the players that left World of Warcraft for RIFT eventually find their way back, the damage has been done for the month of March.
Though subscribers numbers have fallen back down to 11.4 million, overall profit has risen so far this year -- the details of which you can find in the official press release.