You can't use the arguement that because Wii games sell more that they have higher replay value. The Wii has sold twice as many hardware as the PS3 and X-box of course their games sell well. Also due to the lack of quality 3rd party games and having a 10/20 year headstart on Sony's and Microsoft's franchises of course their franchise games are going to sell really well. Just because a game sells well though doesn't mean people aren't selling them back for credit. In my opinion Nintendo games have the least replay value. Most games you can go back and collect all the extra stuff and play local multiplayer but a lot of their games lack online multiplayer (and the ones that do have online multiplayer lack the depth to make me want to play it more then once or twice), dlcs, leaderboards, trophies/achievements.
They are making games like it's still the NES era, unfortunately what made NES games fun is the difficulty and the limited number of continues.
Oh and I don't know what you are talking about, I see a huge number of Wii games in the used game bins.
This is only my opinion.
