Some of this is likely wrong, but I'd say it seems about spot on that COD BLOPS total PC sales are around 2 million units (being Steam only represents 70% of the DD market on PC according to the most recent analysis info, and counting retail). The games after that I do find questionable in some instances.
I love Steam, but we have to consider that recently Magicka made it to the number 1 selling game on the service its' first day while only pulling in ~30K. I think Steam is big, but I question whether it's the juggernaut that many propose it to be.