[jonesb6]

I've seen the phenomenon on Reddit where two identical comments will have completely polar votes. One might have -50 and the other 50.

Someone deduced that it was the time that the comment was created that mattered. If a large number of jokesters are on at one point then their up votes will create the critical mass to push the comment to the top and keep it there.

I also believe that once a post is at the top fewer people will downvote it, either because they are afraid to go against popular opinion or merely respect it and leave it as it is.