I've been of the opinion that Gamespot is in something of a game, to take down Wii scores on Metacritic and Gamerankings. Obviously, it's hard for them to do that with the big AAA games on the system, as publishers would never allow them insight into a games development again, but with smaller titles, especially ones that aren't all over the radar of all gamers, it's an easy way to take down a system's overall score on those ranking sites.
Let's face it, their overall ratings since the Wii has been released haven't made any sense. They rarely jive with any of the other major sites, and are always handicapped by what usually amounts to a mole hill of complaints.
Personally, if I see a game for the Wii on GS that has a score of 5, I just assume that it is probably about a 7 or 7.5. The bias is really pathetic. Once they were the place I went to for reviews, but now I can't take any of their reviews very seriously.