I was always confused by slashdot's filters and the threads in almost every other forum, with Post #18 replying to Post #7 and Post #27 replying to Post #3, but only 10 posts visible per page. Busy people don't have the time to wade through stuff like that, so all you're left with are the trolls.
hn's nested threads built with <table> are so simple that they're brilliant. No horizontal scrolling, no flipping between pages, just click "reply" and you're good to go.
I have no idea how much time and effort pg puts into hn, but I'm sure it's nontrivial. Something as good as hn doesn't get that way purely organically. Also, I would guess that more of his energy goes into the software, not the site's output. Why deal with an issue once when you can build something that will deal with it forever?
It goes without saying, but I'll say it anyway: thank you pg!