I have another problem with the interpretation of lowest and average scores: Metacritic doesn't even compute a score with less than 4 reviews.
That means that really bad games that critics aren't even interested in reviewing won't contribute to the average, whereas games that are not as bad, but for some reason catch more the eye of the reviewers will.
An example is the latest Leisure Suit Larry game that was reviewed by many sources because it happens to belong to a very famous series of games, with dismal results (21%/25% on PS3/360). On the other hand nobody cared much about "Battle Rage:mech combat" on the Wii, so it has only two reviews, both of them are 20% but they don't contribute to the average.
All in all, this means that the higher end of the spectrum has some statistical relevance, and shows that the Wii is getting some good games. But the lower tail and the average suffer from arbitrary filtering of the data, and can't be given any serious relevance.