There was a time in the 19th century where thin, spindly fonts where in vogue for printed books. They were later criticized by typographers and general readers for making books harder to read [1].
The web is experiencing a similar scenario where thin typefaces are being used for body type as it looks modern even though it's making body text less easy on the eyes. In small paragraphs I personally don't mind it, but many sites are now using it for long articles where it's not ideal.
[1] Daniel Updike's 'Printing Types, Their History, Forms, And Use; A Study In Survivals' is a great read.
Everything old is modern again. Cool links. I spent weeks fighting (and mostly losing) to a designer that wanted every website to use no more than a 300 font weight and no italics or other differentiating typography, all because it was "modern and light and airy". Wish I could have been like "Nope, here's people in the 19th century complaining about it" back at that point.
He's using -webkit-font-smoothing: antialiased; With this sort of font it looks terribad. You see this way to often. I've been guilty of it by proxy when another dev comes in and applies this style to the <body>
http://devinhunt.github.io/typebase.css/
PS: I'm on a retina MBP in 1680 mode so your results (and eyes) will vary