Topics appropriate to HN include anything that gets enough votes to make the front page.

That's definitely not true, as the guidelines make clear. Otherwise the front page would consist of controversy, gossip, and fashion, probably in that order.

HN has always been a blend of community voting and moderation (also variously called "curation", "editing", "censorship", "manipulation", and my favorite, "thinly veiled aggression") based on the site's values.