Am I missing something here? What difference does it make which platform sold most copies?

All that figure gives you is an approximation of the number of consoles sold factored against the likelihood of the owner of said consoles to like that game. And the exact figures for the number of consoles sold is already known, so it's a bit pointless.

It doesn't say anything about which console is "better" (not that you can really measure which console is better than another) and it doesn't give any indication of which version of the game is better (not that you can easily measure that, either).

Sony is King! All i know is dat sony is beta dan microsoft, with over a millon replacing there xbox 360s due to hardware failure with having 3 red lights! (tutut)