Unless I'm mistaken, VGC numbers do not account for DD sales, which would only be available from the direct distributers themselves. Taking that into account, no one that I'm aware of compiles DD figures along with estimated retail unit sales.
EA would have to release their Origin sales figures, Valve their Steam sales, etc. As far as I know (didn't bother with a 30 second Google search) they don't release those figures.
It's well known that the vast majority of PC game sales have shifted to DD and that retail copies are for all intents and purposes, a legacy distribution format that does little to extend availability of product to broader markets.
It's fair to say that retail copies of PC games probably comprise less than 10% of total sales, making the monitoring of these figures an extremely poor gauge to measure the current size of the PC gaming market.







