I'm mistaken then; from the block you copy and pasted I misread it to suggest only IE 9 cares about quirks. In my personal use I'd never seen it matter cross-browser before
Of course HN works fine, if it didn't work fine it'd be fixed by now. "Working fine" is an extremely low bar for any site. As a developer you will still want to avoid quirks mode because it just makes your life harder for no reason.
If you don't care your site potentially becomes unusable broken shit outside of the specific browser you develop it on, there's no real use.
https://quirks.spec.whatwg.org/