The game shipped on December 17, but NPD didn't list it among the top 10 PC games for the week of Dec. 15 to Dec. 21. In an interview with Reuters, analyst Shawn Milne of SoundView Technology Group said the game sold about 12,000 units in its first two days, and that there were 30-50,000 beta testers who had free access to the game until Friday (who presumably wouldn't be pressured to purchase the game until that date). However, in a note to his clients, Milne said the game was "off to a slower-than-expected start".
One explanation for the game's seemingly slow start could have to do with the limited distribution it had during its first week, since a number of retailers reported that they did not receive their shipments of the game until just prior to Christmas. So the next report from NPD, which comes out this Wednesday (January 8), will likely have more bearing on the situation.