I will agree to an extent that there are a number of games out there for Wii that are "dumbing things down," but many are just looking for ways to leverage the new technology and provide for better, more intuitive control interfaces that never could've exist before. But I will also agree that some people here make a big deal about the traditional controller now and how confusing it is, yet never seemed to have an issue with it last gen.
Also, Wii Music probably takes more skill than Rock Band or Guitar Hero because you need to be creative and you need to have some concept of musical knowledge to succeed. When playing your typical rhythm game, the game instructs you 100% of the time, telling you exactly what you need to do and exactly when you need to do it. Those cues don't exist in Wii Music at all, thus requiring players to listen to the song and determine what their part is, recreate that part, and finally improvise on it to give it a unique feeling. It's not something you could understand unless you played the game. Most people hated on Wii Music not because it was terrible, but because they were terrible at it.