That method you mentioned can't work in practice, it would give more errors than VGChartz or NPD have in their data... All I'm saying is that any method which aspires to be somewhat accurate must include some subjective factors.
You yourself mentioned that some retailers have to be weighted. Do you agree that those weights will be heavily dependent on the demographics a game attracts? To use the same example, what would happen if you assumed Ninja Gaiden 2 and Wii Play were equally distributed among shops? I'd bet a lot of money that you'd get massive errors on at least one of those games' numbers. It's just not possible to have a reasonable estimate without accounting for the vast differences in sales distribution of different games. The choice is then to either have wildly inaccurate numbers generated by a rigorous process, or more accurate numbers generated by a mixture of objective and subjective methods. I know which one I'd choose (i.e. I wouldn't bother with the former).
I can't comment much on the rest that ioi said, because I'd be guessing too much... What I'm saying is that we shouldn't be surprised that there are subjective factors in tracking sales which may easily be called guessing.
My Mario Kart Wii friend code: 2707-1866-0957
