I think there's a bias against funny and amusing comments, and I think it's appropriate. The internet is an inexhaustible source of mildly amusing, even fairly funny stuff. There's a limited amount of room on the HN front page, and it shouldn't be wasted on humor of the quality that can be found in vast quantities all over the internet.
If you want to be funny, be interesting at the same time. If you can't, then save the joke for reddit.