Well if I didn't, if I just tried to give a song a rating on it's own like out of 5 stars or 10 stars or whatever, I'd probably just give almost everyone the same score each round.
Plus I just don't think I'd be that good at doing star ratings like that. I have lots of "10s" even though I like some of those better than others, and that might not even make sense to people.
Also, pretty sure I know what #2 is as well.