Of course Valve games are going to sell like crazy on Steam. CoD4 on the other hand will absolutely not sell via DD anywhere near as well as retail.
And once again, you bring your speculation and imaginitive calculations into how much CoD4 sold on pc. As of June of last year CoD4 had 10 million units sold, with the 360 version doin the best. If we were to assume the PS3 version were to have sold 1 copy and the pc version sold 4,999,999 copes to the 360's figurative 5,000,000. That would mean it would have to have sold another 10 million copies on pc in order to reach the numbers you gave. So in the amount of time from July to now, the same amount of time from launch to June, COD4 would have increased its sales rate two fold. Piracy would be the only thing giving credence to your number, but even then that would be stretching it. Also, you seem to assume that sales of the 360 version have stopped as well. 6 months after the release of CoD4 the 360 version had sold the most. That is unlikely to have changed.







