Comments on presentation are quick and easy to make. They show up soonest on a submission, and since they're at the top, collect upvotes. Comments on content take longer to write, end up below comments on presentation, and receive fewer upvotes.
HN should have randomised ordering of presentation of top posts, with a sort of simulated annealing technique that fades over time, so leaves are sorted to the top based on the branch total vote count after some hours.
