edw519 regularly says something laugh-out-loud funny that also helps the conversation along, and scores a bunch of points. Other people often say things that are only slightly funny and have no other value to them, and score a bunch of negative points.

Funny and contributing = upvoted Not funny and contributing = upvoted Funny and not contributing = downvoted Not funny and not contributing = downvoted

Don't make the mistake of thinking funny/not funny is the deciding factor.