I'm not a Michael Jackson fan, but as a musician I have to say that the main thing that really matters to me about any occasion is the music. My wedding was all about the music, I'm sure my memorial service will be as well. The people doing the music, readings, etc. won't be celebrities, but since that's who Michael Jackson associated with, it makes sense that it's all celebrities there. I think it makes total sense to have a concert to memorialize a musician - it wouldn't make sense to me NOT to make music a major focus of the service.