All polls work this way. When someone votes the forum acts as though its a new reply even though its just a vote.
So when you see the threads with polls always towards the top its just cause someone voted on it whether they replied or not, hope that makes it a little less confusing if it ever was.
I have no idea... just by looking how we seem to have stalled on the initial 4 characters, however, I'm not sure they'll be putting more into the mix anytime soon.