His response to me (w/ irrelevant stuff redacted):
The short answer is that HN's goal is quality, so that's
what we optimize for. Optimizing means trading other things
away. One thing we're willing to trade away–if it's a clear
win for quality–is fidelity to the original submission. HN's
focus should always be on the content, and the details of the
original submission are of little interest compared to the
subject at hand.
HN isn't a purist's kind of place. Our goal to make the
front page and the threads as interesting and substantive
as possible. We change a lot of things to serve that
principle. If we knew how to serve it better, we'd happily
break more crockery to do so.
Someone (perhaps a purist!) will object that terms like
"quality", "interesting", and "substantive" have no precise
definitions and are in the eye of the beholder. True, but (a)
they're not arbitrary either, (b) the alternatives suck, and
(c) someone has to make the calls. We don't get them all right,
but we do try hard to correct mistakes, and I'll defend the
principle any day.
1: dang = Daniel Gackle, HN's moderator. http://blog.ycombinator.com/meet-the-people-taking-over-hack...2: Original thread: https://news.ycombinator.com/item?id=7747401