@Paul Warren: You're pointing out how the reviewers are irrelevant, since they don't seem to reach their audience with reviews - gamers. The problem with reviews is, that the reviewers look the games with technical aspects in mind, while gamers are looking for fun. Maybe you're delivering a deeper message, but i can't see your point.
As for the new, original IP:s, if you try to prove something, you can't "just pick the games you want".
Let's look at the old IP:s first, 80:s Donkey Kong, Mario, Metroid, Zelda; 90:s Fire Emblem, Pokemon (or was it 80:s), Starfox, F-Zero; 2000:s Animal Crossing, Brain Training, Big Brain Academy, "Wii series", Pikmin. And those were the games that have had sequels and are having still today. There's number of games that didn't (haven't yet had) have a sequel, such as Doshin the Giant, Geist, Eternal Darkness. And there's a number of new games, that use familiar characters, like Mario Party, Wario Ware, Luigis Mansion, Partners in time, Paper Mario, Tingle's Rosy Rupeeland, Tetra's Trackers, Super Princess Peach. And coming titles like Disaster and perhaps even Project Hammer. I don't know what do you expect from Nintendo. They release a fair amount of new and old IP:s, it's just that making games for 30 years, eventually result to having a shitload of IP:s, that would be a waste for not to use.
So, Wii has other games than just Wii Sports to justify the purchase. What a surprise. Besides, Wii Sports attach rate is high in Japan, so it definate is a game that people want to play.
As for the PS2, we should check out the number of games "scoring higher than X" after Wii has been in the market for 8 years. Current comparision is very stupid between 20 months old system and 8 years old system. That would be like proving how much better launch PS2 had, since it has after 8 years in the market, thousands of games.
I believe the question wasn't about whether you like the games lineup or not, but how did the high metacritic score effect system sales. I think it was pointed out by Happy Squrriel that it wasn't the deciding factor between XB and GC.
Oh, and i don't know about Disaster or Wii Music for what kind of score to expect, but the Animal Crossing games have metascores of 86 and 87, and the Wii game propably hit the same range, so it is noticeably better than Wii Sports score.