You are completely forgetting digital distribution. Even if only 6 or 7 million of the 10 million shipped have sold, that is only retail box sales. The rest of that $650 would be through digital services such as Steam.
Typically in today's market digital PC sales are much higher than box sales. As high as 6:1 digital over box sales.
I didn't forget digital sales, those are included in the 10 million shipped, just like EA's 12 million shipped copies of Battlefield 3 two weeks ago encompassed 8 million copies sold through both physical and digital sales. PC digital sales are often more than physical sales these days, but not by huge amounts. It's unlikely that the total physical/digital PC sales match or exceed those for the 360, which is likely where most of the sales are. The 360 has 3.55 million sales so far, and the PC has 1.26 million physical sales, so another 2.29 million sales in digital would put the PC sales on par with the 360 sales, which would make the total sales across all platforms be 9.12 million. It's unlikely there are that many PC sales though.