HN is not Reddit. Plenty of people make humorous or entertaining comments, but distracting joke threads full of obvious one-liners and no real content aren't generally welcome.
There's actually a really interesting discussion on Quora, I think, about why they had something along the lines of a no-humor policy.
The problem isn't that people are humorless– it's that when you reward people for humor (often resulting in puns and pithy one liners), after a while, people start competing to be as funny as possible– and that's all that ever rises to the top. It crowds out more deliberate, thoughtful discussion.
I love humor and comedy myself, but it makes sense to me why a discussion forum might deliberately choose to discourage it.
And you know, it's interesting to think about why that is, and how that helps anybody.
Have you ever gone onto a blogpost about procrastination and found the "I'll read this later" comment, and the "I'm here reading this instead of working" comment? Are those comments ever valuable?
It makes sense to downvote them to the bottom, so that people who go looking for them can find them, but the discussion is kept as fresh and relevant as possible.
we are getting meta but I think these type of comments are of a different breed. These do not provide any meaningful (or value) to the conversation nor are related to the subject, on the other hand the "tl;dr" was totally related to the context of the article, and a nice pun intended for the sense of humor.
Also it was how this whole conversation started, although really tangential to the OP; which encouraged a conversation.