It originated in the 20s and 30s in the Bauhaus, Herbert Bayer http://en.wikipedia.org/wiki/Herbert_Bayer was one of the more prominent supporters, designing typefaces that contained no uppercase letterforms at all. He even experimented with designing entirely new alphabets that were phonetically based.
Jan Tschichold was another Bauhaus guy experimenting in the same realm. From Wikipedia: "Between 1926 and 1929, he designed a “universal alphabet” to clean up the few multigraphs and non-phonetic spellings in the German language. ... The alphabet was presented in one typeface, which was sans-serif and without capital letters."
It's interesting that it was born out of choices made to German, where they have many more capital letters in each sentence than we do in English. Regardless, it's clearly a stylistic choice, and one that the OP might even have to work harder to maintain, if he is accustomed to writing in sentence case.
There's that old saying that you must first learn the rules and then you can break them. That is exactly what is going on here, and the OP isn't unique in this. Throughout my time at design school many of my teachers, who had been educated by Bauhaus instructors, would email in only lowercase—they adopted the style. And others have adopted it from them (here's one of my design school friends' site: http://traceychan.net/ where she has).
I quite like the style myself.
To a fast reader, without visual cues it is a jumbled mess. I gave up after forcing myself to read three sentences.
You would be right if his goal was to impress someone but I doubt that was intention of his blog.
I guess we all have our little pet peeves :-)
I'm not exactly willing to die on this hill, though -- the article is not very good in any case.
edit: removed all capitalization so you can reply to me about how you won't read my comment because i am too lazy to capitalize a word.
Lack of capitalisation interrupts the way you read a block of text. People make poor design choices all the time, and this is one of them.