Well I never looked at the stars as a skill rating, just a score rating (which is what it is). I see what you're saying, but you can still determine "skill" of a song by the percentage and note streak you end up with. But after a while the star system almost becomes meaningless since it ends at 5 and your scores will start going well above that. That's why I like how scorehero added 6, 7, and 8-star ratings.