[printer]

Every font is designed for a purpose. Serif fonts are designed to help the brain recognize the different letters. Comic Sans was designed to be used informal. Helvetica was designed to be used in signage. Verdana was designed to be readable from (72dpi) computer screens. And so on.

So as screen resolutions increase a serif font can help the brain to recognize small letters increasing readability.

[podperson]

Serif fonts are designed to emulate Roman inscriptions, which had serifs to help water drain out of them without wearing them out (and thus reducing maintenance costs). The brain stuff is at best speculative and not backed by any data (and in any event is a post hoc rationalization).

In general, readability tests (per the original article) have produced equivocal results which seem to show mainly that people prefer the fonts they grew up with.