Sans serifs are overused because they look better on low resolution screens. If you haven't had to use a low resolution screen in a while then you are one of the privileged few.
At small sizes, like 8–13px, sans-serifs look better than serifs. And user interfaces and websites used to be that size.
But for 16px and up, which is what websites of today use, serifs are perfectly fine even on 1× displays (though sure, they’ll look better still on higher-DPI displays, but so will sans-serifs).
I should clarify that it depends on the font. Sans-serifs tend to have fairly even stroke width, but serifs tend to have more variable stroke width, and if the thin is too thin, you get a terrible font. That’s a common shortcoming of serif fonts, and Garamond demonstrates that, being quite unsuitable for screen use below 20px, maybe even 24px. Others like Georgia don’t suffer that weakness.
Are you sure that "websites of today" use 16px or larger universally? HN appears to use 9pt Verdana, which I believe is equivalent to 12px on my Windows system if my math is correct.
Georgia is a terribly underrated font. I'm sure it's heavily hinted to look good at small sizes, but even at large sizes it has an elegance that is lacking in e.g. Times Roman.
This sounds like it ought to be a job for pixel-density media queries [1] in CSS. I doubt this happens often if ever though, because designers. Anyone seen this approach in the wild?
I guess I specifically mean the default browser serif font. There are sites that consciously choose a serif typeface to convey some sense of "we are serious content," but you may notice that none of them use the default browser serif font (except as a last-step fallback).
If I see default browser serif, my immediate thought is "either this is an amateur or something is broken."
I don't have data to back it up, but I've understood from typography gurus that sans-serif fonts are great for signs, short blurbs, etc. But for long (multi-paragraph) reads serif fonts reduce eye fatigue. I think blogs typically fit in that category.
