I'd agree that dang's role is key to HN, though pg also set things up in terms of direction and focus. I've been diving into some of his comments on HN, goals, initial direction, and lessons learned. These are informative and address topics, questions, and issues frequently raised over the ensuing 17 years. Both execution and constitution matter, IMO.

What you discuss regarding the enabling mechanisms of college towns is fair commentary, though it should be noted that there are other money faucets which don't create the same effects: natural resource extraction economies, excluding the rapid boom/bust variants, don't give rise to the cultural aspects of a college town. Tourist attractions may, if, say, arts and culture are significant elements of this (say, a Sedona or Ashland, OR, or Bayreuth), though it can be difficult to disentangle tourism from other elements for larger destinations (Disneyland and Hollywood in the Los Angeles region, San Francisco as distinct from its economic and tech-sector activity). Heavily merchantilistic cities can draw wealth, but are less effective with culture (again, trying to isolate for those without a major academic centre, so NYC, London, and Paris would be confounded examples). But a Hong Kong or Shenzen or Dubai or Singapore whilst having an extraordinary merchantile / trading role, does not have a commensurate cultural or academic one.

And at the other end of the scale, you can have college towns which are too successful. I'd put Stanford and environs here: Stanford, Palo Alto, Menlo Park, and Los Altos, say. These are so wealthy that the cultural amplification of the educational institution is dampened by the lack of affordability of the region (housing, etc.). Several of the US East Coast college towns have similar issues.

There's still something particular about the college town dynamic, and I think the points I've raised are fairly key to it.

Regarding Reddit:

The larger encompassing community was useful for a time, but with brigading and even just having a smaller sub appear on the front page or cross-posted to a larger one, the local in-group culture could very easily get overwhelmed. (This is hardly specific to Reddit, and there were examples of trolling and other cross-newsgroup attacks on Usenet.)

Reddit does little to foster conversation. I still miss Google+'s dynamic of having a Notifications pane which showed all threads in which there was ongoing discussion (whether it directly involved you or not), and both presented those threads and enabled replying directly from the Notifications pane. This meant that:

- Conversations could continue for a prolonged period of time. Days, weeks, even months or years in instances. And do so productively. (Yes, the thread host would have to delete spam and trolls, but a well-tended thread was a delight to behold.)

- Other participants would be made aware of the ongoing discussion, and could choose to rejoin if they wished. Or to opt out (mute the thread). Again, with a principled and intelligent host, this could result in long-ongoing discussions.

On Reddit, a comment reply generates a notification only to the author of the comment replied to. There's no sense of a thread-notification (or even some smaller region, say, the three or five preceding comments' authors). This means that conversation tends to die rapidly on Reddit.

For HN there's a similar issue, though with the "Threads" link it's possible to see if there's been general response to a specific comment of yours. There's no notification mechanism, and unless a third party is higher up on the thread, they're not going to see the activity within their own Threads view.

The G+ mechanism can be abused, of course, and is again affected by scale. On G+, a "thread" consisted of an initial post and up to 500 replies, a limit I saw reached occasionally. This limited total participation, though it seemed to be sufficient for most discussions. I'd make a practice of splitting off sub-discussions or linking a continuation thread to preserve integrity of the origin discussion. With 500 comment slots, 20 people would have an opportunity to comment 25 times each, which is reasonably comprehensive.

One feature Reddit has that's underutilised (and underpowered, in terms of features, notably search) is the built-in wiki. That could serve far more than it does as an informational repository. There are some subreddits which make good use of the wiki, far too many which ignore it completely. Not being able to search the wiki means it's a bit of a roach motel (text checks in, it never checks out), but ... the concept is useful.