I think the karma system can also be a contributor to this. Any comment you make has the chance to get a few upvotes, regardless of how little it contributes to the conversation. So people just spam comments to get a few points here and there.
This phenomena can be seen in forums without karma also but i think in places with karma it is usually worse, worst offenders being digg and reddit where everybody tries to make a silly joke as those are easy points.
A better algotithm calculating the karma as an average over all your comments maybe could help..
I have mixed feelings about karma. It's nice to have filters that bring (mostly) better comments to the top, but I think it results in more silenced voices than it does posts-for-karma's-sake.
It's validating to get a few upvotes, but more than that it's disheartening to spend time on a comment and recieve no feedback whatsoever.
I'm an outgoing person, but I find myself shying away from commenting on HN for that reason. Admittedly, I don't usually have some brilliant insight, but it does make it harder to feel like part of the community.
It might also be interesting to rate-limit commenters (perhaps based on their previous upvotes per comment).
If you are new to HN, you may only post one comment per week.
The "better" (as measured by karma) your comments are, the more comments per week you may post.
This might make commenters consider whether their comment is really so important that they sacrifice another opportunity to comment in the future.
The "average" (on your user page, seemingly over your last few comments) seems to matter more for how high your posts appear. I've found myself deliberately not replying when someone makes an interesting reply to a comment of mine a few days afterwards, because posting that reply brings my average down. Which is definitely a bug.
It would also favour the short and succinct over the long and rambling. Which sounds like a good thing, if you believe that useful information can be distilled losslessly.
This phenomena can be seen in forums without karma also but i think in places with karma it is usually worse, worst offenders being digg and reddit where everybody tries to make a silly joke as those are easy points.
A better algotithm calculating the karma as an average over all your comments maybe could help..