I disagree here. Just the sales numbers would be accurate to gauge what's been sold and more accurate than what was shipped for instance.

The download stats - I know from even my time/experience that I downloaded the same thing multiple times due to either reformats, updates that went wonky or me screwing up my own install and starting back again with a new install.

So those numbers are a bit inflated. And in some cases, not wholly reliable - some of the best apps got minimum downloads for some reason.