You seem to think that a lack of usernames means a lack of community, and this is not remotely true. Anonymous forums have been around for decades and have been quite successful.
It's tangential to the main point that HN is one kind of forum and not another, but I'd be curious to know some examples of what you're talking about. I don't think I've heard of one, and I have heard of counterexamples. In fact I ran across a famous one yesterday: https://books.google.com/books?id=pwo5DwAAQBAJ&pg=PT126&...
Edit: that link no longer seems to work, but it was to a page of the book discussing an anonymous community that the WELL tried in the 80s, which quickly became abusive.
I know it is mostly a bunch of boring kids who like to be edgy to piss people off, but for me 4chan is an example of a successful community on what it does. I really think they far surpass HN in many areas : creativity, being in touch with popular culture/trends, willingness to take action,self-censorship, etc.
