I don't comment much on topics where I feel I lack enough knowledge to add anything to the conversation, even if I find the post or conversation interesting. As a result, I only really comment on perhaps < 2-3% of the threads I read. I imagine this is similar to a lot of other HNers and it helps keep the signal-to-noise ratio relatively high.
With no snark intended, it boils down to: "If you have nothing to add, don't."
1. >> even if I find the post or conversation interesting
The "interesting" bit is important. There have been (less popular) threads where I have noticed funny for funny's sake comments being left alone. A trending topic is a dangerous topic for comments where your comments will be read by more people who are likely to feel that it does or does not add much "value".
2. >> "If you have nothing to add, don't."
I don't think that sentiment can be expressed any differently, snark or not. :) You could have been more blunt too. I think that point's very valid within the HN subculture.
Irony is, both these takeaways are something that one picks up "after the fact", which in itself is ironic.
With no snark intended, it boils down to: "If you have nothing to add, don't."