On my first jam (LD46) the ratings actually matched the downloads quite well.
I think this has to do with the 8000 participants that didn't finish a game. Maybe they are the shadow players.
Anyway regarding the rating, there is no next round. GMTK's jam has one where he personally plays the top 100 to pick the 10 best, but he also gives out goodies and want's to make a good video, so it's understandable.
Jams usually are participant rated and there are no judges (the hosts are the secret police that are supposed to boink the cheaters and foul players). Full democracy here.