Well if the Xbox has multiple LIVE accounts, then it is indeed possible to have more players playing the game than it actually sold.
Still that should only account for a few 1,000 entries.
Anyway great sales, looking for a 300k+ week one, which should definitely lead to 700k lifetime sales:
http://gamrconnect.vgchartz.com/post.php?id=4523759 (third table)







