I doubt age had much of a factor. The same people who voted are the same people who did the reviews. The reviews for SMG were all high, so it can't be that they didn't like it. I personally Like most** types of games and I had more fun playing CoD4 and Orange Box than playing SMG. I never got to play Bioshock though.
Also about Multiplatform thas, I don't think they had like CoD4 360, CoD4 PC, CoD4 PS3 all in one category. Im pretty sure it was just CoD4 as a whole because they're the same on all platform. Same with Bioshock being the same on 360/PC.