That's awesome. Are these just comments with a high karma, or is there some other magic going on?

Seems like a combination of length and karma — or maybe length and karma just happen to correlate? There are short ones in there too. Hmm.

My guess is it's a simple time-decay-weighted karma-based formula. That is, karma * e ^ -age. "Best" vs "top" may be the difference in net karma vs gross positive karma.