I don't think graphical limitations have much to do with it at all...especially given that so few developers don't even bother looking at the Wii's limit, never mind trying to get to it.
The "evergreen" titles that you are talking about sell for such long periods of time because they have a wide appeal, and good word of mouth between communities of Wii gamers, but they were not hyped before release.
Pre-launch hype sells a hell of a lot of games to the "hardcore" crowd, I would say selling a lot to people who might have passed the game on if they had more time to think (ie feedback from actual gamers that play it, rather than reviewers) I know I would have bought Super Smash Bros. Brawl had it launched here in Europe nearer to the American release, instead with a couple of months to think it through I decided against it. This wasn't really due to negative feedback from gamers as I didn't hear much negative about it apart from the terrible online, but more that I decided it didn't really appeal to me.
