Those sale number for ME2 are way down, VGChartz has it at 900,000 in it's first week and 1.4 mil after a month.
Heh, VGChartz. There's a reason Wikipedia don't accept them as a valid source. EA's own figure was 1.6 million sold including all PC after three months, though it isn't the first time they've been caught out that way (similar thing happened with Bioshock). NPD is a limited source as well, but far better regarded than VGChartz.
For What it's Worth the methodology I used to get the figure was:
ME2 800k NPD (2 months 360)-> 1.6 million total sales after three months inc PC (per EA quarterly report).
DAO 1100k NPD (2 months PS360)-> 2.2 million total sales after three months inc PC (extrapolation).
DAO has almost certainly sold more than 2.7 million copies by February (reason: initial shipment was 2.7 million per EA quarterly report but it had shipped 3.2 million by February). That suggests PC sales of 500k + proportion of 2.2 million + whatever else has sold since = estimate of roughly a million.
There are a bunch of assumptions there of course, but I'd say the 1 million estimate is a fair one.
When you're extrapolating, are you taking into account that NPD is NA only? Worldwide doubling the NPD number is a pretty good estimate. If DAO indeed sold 1 million on the PC (which I don't believe) they'd be a lot more eager to support the PC (that's 50 million in revenue, surely worth a top down view).