Technically World of Warcraft: Cataclysm shouldn’t class as a game in its own right as it’s an expansion to an existing game. But in terms of sales, it still counts as a release and therefore can break sales records. And it’s with little surprise that we find Blizzard’s latest MMO expansion has broken PC game sales records.Having been released on December 7, World of Warcraft: Cataclysm managed to rack up 4.7 million sales by the end of 2010. That sets a new record for PC game sales in a single month.The huge sales were helped by the fact that Blizzard did a simultaneous release across the United States, Canada, Mexico, Argentina, Chile, Europe, Russia, Southeast Asia, Australia, and New Zealand. Korea, Taiwan, Hong Kong, and Macau followed two days later. As for how the actual sales broke down, 3.3 million were pre-orders shipped on day one, the other 1.4 million were sold during the rest of December with many likely finding a place under Christmas trees.While 4.7 million copies sold may seem like a lot, it only accounts for just over a third of the World of Warcraft player base currently estimated at more then 12 million players. It’s inevitable that many of those players will end up purchasing the Cataclysm expansion eventually as they continue to eat through the content offered in the original game and other expansions.Read more at the Blizzard press release, via 1UPMatthew’s OpinionBlizzard can seemingly do no wrong with its money-printing MMO. Everyone at the company and at owner Activision will be extremely happy with these sales figures. Inevitably the focus will soon turn to the next expansion, but just as importantly discussions as to what game will eventually replace WoW.As we have seen with other popular MMOs like Everquest, even when subscriber numbers start to drop off many years after launch it can be worthwhile supporting a game with continued new content. WoW will still be online in 5 years time or even 10, it may be the case that we have a WoW 2 by then, but the original will still have a dedicated player base Blizzard would do well to support.