I agree with HunterIXC among others; Blizzard wants to milk WoW (I admit I hate it; for me, it ruined the Warcraft setting) until it's totally dry. Yes, SC2 is on the way -Betas have been released not much ago- and looks good, but it seems their main source of profit is WoW and everything related to it; from RPGs to that movie that's also on the way, including all the in-game stuff that you've to pay for.
Anyway, it seems WoW's end is looming on the horizon (however, it certainly will not happen tomorrow), despite they said they expected it would last still more years and their plans of releasing new expansions if people still plays it; see, for example, how the world will be redone in Cataclysm (and new race combinations (night elven wizards, when according to some sources they could not handle arcane magic?
)).
I suspect they're taking positions to be ready for WoW's -slow- downfall, releasing SC2, and after it DiabloIII and finally that new MMO it's rumored they're making.