What does that mean? It means that an expansion pack is the fastest selling PC game of all time. Oh, except that doesn't change anything. Previous fastest-selling title was, well, Wrath Of The Lich King, which sold 2.8mil on day one. Apparently over 15,000 people attended Cataclysm launch events across the world, and the subs base for the game now sits and 12 million. It's still an amazing thing, given that I can remember people tutting sceptically over Blizzard spending all their money on making that game in the first place. The lesson here is: don't bet against Blizzard.
It must be nice to be rich.