It's not Wrath -- the game's been selling like gold encrusted hotcakes since launch. There could be an upcoming shakeup in Activision's leadership (is Bobby K on his way out?), or it could just be that as well as Activision did this past year, the rough economy is hitting them hard, too.
At any rate, this will likely be just a bump in the road -- Activision is poised to become (if they haven't already) the biggest publisher in the game, and as you can see from this graph on their website, the stock is already back up above $9. We don't know what the reason is for this quick drop, but everything else we've seen points to a bright future for Activision-Blizzard.