You can try emailing pg, but that's more of a rumor as it's unclear what account deletion would do. Certainly it would not remove your contributions on HN.
It'd be nice if there were a terms of service stating this when signing up.
You should assume it when signing up for any site unless otherwise indicated.
Assumptions are the root of all evil.
If you use the search, you'll find that to delete your account, you need to email pg. I've done it before. He'll take care of it.
Now why would you ever want to do that? :P
I guess he is frustrated and (possibly) read few productivity blogs. :)