Setting aside the relative merits of 12pt vs 16pt font, websites ought to respect the user's browser settings by using "rem", but HN (mostly[1]) ignores this.

To test, try setting your browser's font size larger or smaller and note which websites update and which do not. And besides helping to support different user preferences, it's very useful for accessibility.

[1] After testing, it looks like the "Reply" and "Help" links respect large browser font sizes.