12pt Times New Roman is the standard for publishing, so that's become the go-to size for a lot of websites. It was plenty big on 800x600 displays, but I agree that it's generally too small for today's resolutions. However, the solution isn't to pick a new, slightly larger point size and just set everything to that, it's to use media queries to set an appropriate size for whatever medium the content is being displayed…
Readability is useful, though it's not painless to use on most websites. I've said it before and I'll say it again: one of the pleasant surprises of seeing TBL's original WWW documentation posted to HN last year was how readable plain, unstyled HTML markup is. It's almost as if we have a need for two platforms: an unstyled user HTML reader for long-form works, and an HTML+Javascript applications platform for interact…
And readable on any computer, with any OS, with any browser, whether it's going to a screen or a printer or a speaker.
It is baffling why text heavy sites (where the product is the text) get display of text so wrong.