I'm surprised. Those comments must be wrong. We respond to this at hn@ycombinator.com all the time.
HN doesn't delete accounts. We do delete specific posts that people are worried about getting in trouble from. The reason is because deleting an account and all its comments guts the threads that account participated in, which is unfair to the other commenters in the discussion. The threads are community property and we have a responsibility to preserve them. PG wrote about this here: https://news.ycombinator.com/item?id=6813226.
Our approach tries to balance that concern with individual needs. Sometimes people post things they later regret, e.g. personal or employer info. In such cases we're happy to help by redacting or deleting the comment. But we do it on a case-by-case basis. That way people can get their specific concerns taken care of, but the community history remains largely intact.
We do intend to implement account renaming, which should resolve most remaining concerns. But it isn't done yet.