One thing that I don't think is widely appreciated about HN's design is the balance it finds between information density (i.e. fitting a lot on the page) and minimalism. If you try to move that needle in either direction it makes things worse: more cramped or less informative. Most attempts to redesign HN add tons more whitespace, but this lets you take in fewer stories at a glance. Of course, tastes vary widely and many people disagree.
The link to Reddit is genetic, since pg gave the original idea for Reddit to Alexis and Steve, and only made HN when his feature requests were no longer at the top of their list. Presumably that is also how the idea of keeping HN small got started :) There was also an early version of Delicious that looked a bit like what HN and Reddit later became.
I usually always get my sister to beta test. She knows enough about computers, but when it comes using computer programs, she can get lost sometimes. So if she questions something, I change it until she has no more questions.
I'm pretty sure the one who designed HN just had a preference for a minimalistic approach and everyone thought it was great, and it has stuck since then. No point in ever changing something that just works. And you can't really do much more beyond "minimalist" -- maybe "brutalist" but it isn't something that is favored by everyone.
- The creator (((pg)). I bet the imbalanced parentheses gave him a stroke even if he didn't read this. Voodoo stuff.
- The audience (who they are, what they come here for, all the site is not that makes them return): mostly people who are accustomed to text as a medium of communication (code, docs, books, articles, papers) and might prefer it to other media.
You might like http://textfiles.com/
It may have taken a few cues from Reddit, there are some really substantial differences between the two things.
You must be kidding.