I think I'd need a larger data set to know anything for sure. I'm not one to scold for humor and bits of play on the site, but I think what sets us apart from reddit and those God-forsaken 4chan users is that we do not have a culture of humor, but a culture of enjoyment in logical strength. Humor is fine, but only as long as it is left alone and doesn't affect the discussion board. But the way HN users compete for logical strength and correctness in observation seems to improve the general enjoyment and quality of HN far more than any humor could. No one needs a dry, lifeless site, but it seems HN accomplishes life by more sophisticated and fulfilling means than any other forum, and we won't resort to stupidity like others did.
There's also the possibility of the placebo effect. I agree with donnyg107 in that it'll be a while before we can begin to form a solid "yes, it's better" or "no, we're Reddit" answer... if you're looking for more insightful comments, that's what you'll remember more of (the same way you remember consecutive red lights, but not green ones).