Having played both, I can tell World at War is much, much better than Medal of Honor in the multiplayer department. Graphics and sound are about equal, but World at War's online multiplayer is really good.
I would give World at War the edge in the graphics department - even with Medal of Honor running a 60fps with tons of bloom. The models look a lot better in the former and it has a much grittier look all around that's a bit more aesthetically pleasing in my opinion. I agree that WaW crushes MOHH2 in multiplayer hands down - even without 32-players.
I don't think the game flopped as big as you think it did. Of course, I'm not doing any of the analysis that you've done with the number of online accounts.
How much do you guys think would be a reasonable amount of copies sold for the Wii version?