Having line-height: 1.6 on HN would go a long way in terms of readability.
It's important not to go down the slippery slope of adding too much functionality, in my opinion - look at Reddit, for instance. Structurally, very similar to HN, but I'd say it adds a little too much control and detail to the end user. Do I need to know a comment's exact karma rating, the ammount of users online in a subreddit? Does there need to be two different submit buttons? It goes on and on...
I don't think browser vendors are the right people to blame though. Their job is to give the designer enough control and they mostly succeed or sometimes don't (https://www.smashingmagazine.com/2012/12/css-baseline-the-go...)
But you certainly cannot expect them to come up with optimal default working for every single site out there.
So setting proper line-height has to remain the site's responsibility. And something as simple as unitless 1.4-1.6 would improve readability with any "regular" font.
Given that HN isn't exactly famous for using fancy fonts, which isn't a bad thing at all. ;)
Apparently HN is using table layout and `line-height: normal` is set by UA on any table. This is the first time I can't overwrite it by setting it on `body`.
This just breaks anything I know and only leads to frustration.