Past growth is not a real indicator of future performance for WoW. Sooner or later they're going to reach a saturation point where no more customers exist in the market that want to purchase their product and they'll go into negative growth as existing customers cancel their accounts.

If WoW opens up new markets then the potential for growth towards 13M exists, but otherwise I'll be very surprised if they ever reach it, let alone this year. I'm not even sure what markets remain untapped - do they have WoW in India already?