The idea is that comments are for interesting and insightful discussion about the link/topic. From the guidelines:
"Please don't submit comments complaining that a submission is inappropriate
for the site. If you think something is spam or offtopic, flag it by going to
its page and clicking on the "flag" link. (Not all users will see this; there
is a karma threshold.) If you flag something, please don't also comment that
you did."
Your quote does not support your claim that the comments are for interesting and insightful discussion only. in fact, there are some untold guidelines that you must abide by to not be voted into the grey oblivion. One, as the grandparent found out, is that you must only post things that others to deem beneficial. The only yc-sanctioned method of showing support is to vote up. Another strict one is no humor, even if it adds to the conversation.
We've had the discussion before, but humor can get modded up. It just needs to actually funny, as opposed to just the poster thinking it's funny. (You're not as funny as you think you are.)
