> Part of the reason for that is the common interest in a shared niche. However, I believe that most important factor by far is the lack of up or down "voting" buttons.

You may be underestimating the positive impact of "niche" context and overestimating the negative impact of karmic systems.

If it were the case that the more significant factor was the karmic system, then comment threads on specialized blogs and newspapers would have historically been about equally weighted in terms of a metric of quality content density.

My expectation based on anecdotal memory is that we would find a much more significant ratio of high-quality comments on specialized blogs than on newspaper websites.

In this case, it would be the context of the opportunity to comment that makes the difference. I wonder even if the technical stodginess of phpBB systems contributes to the quality of discussion by presenting a higher inconvenience of usage.

My thought is that a newspaper or aggregate site tends to attract users who are seeking an opportunity to comment that is separable from any particular topic or community of interest, and that specialized discussion sites tend to attract users who are seeking detailed information and who (due to the relative obscurity of the site) can find the act of commentary rewarding only insofar as they imagine it to improve their social status within an imagined community with which they feel affiliation. If they admire recurring & recognizable users who produce good commentary, and imagine the other users to be like themselves, they will be motivated to seek reward and recognition by contributing substantively.

I want to recognize anonymous message boards, briefly, just to say that I have very little experience with them, and can't speak about them usefully. Useful commentary can occur in that context and my thesis as it stands does not account for that, but the topic isn't mine to develop..

I am not sure that aggregate commentary sites are inherently doomed, but there may be a threshold to the message volume where the comments become more akin to the roar of a wind. I can present as a relatively positive example the /r/spacex subreddit on reddit, which has had some reasonable success in terms of maintaining the quality of commentary. There are, of course, other such subreddits. In /r/spacex, the important factors seem to be (a) that people visit the subreddit for the sake of linked external information, (b) the recognizability and frequent participation of a key moderator, (c) the recognizability and occasional participation of identified individuals from SpaceX, (d) the pseudonymous participation of current and former SpaceX employees, and (e) the strength of the user contingent which has topically relevant work experience or education all seem like significant factors.

It was in /r/spacex that I first heard the phrase "low effort comment" used to describe the type of commentary that is discouraged. It struck me as especially pertinent in that it summarizes what I generally feel about making comments on yc news. One can of course put a lot of effort into comments that are not seen as very useful, and I have the bad habit of wanting to opine about things of which I have no deep topical knowledge. Such comments are inherently less valuable than they might be if I had such knowledge. However, if the imagination of a community can induce a degree of inhibition in the commentator, it allows a much greater opportunity to reflect upon the value the comment in a "listener perspective" mode, probably altering and informing both the structure and content of what is written, and it lessens the chance that replies will be posted simply so that the respondent can enjoy the experience of (imagining) having said something significant.

Significant meta irony is available to my readers across a wide spectrum of impressions and responses. My apologies and you are welcome, depending.