Where are those 20 page essays on the web? The typical blogging format seems to be 2 paragraphs and a link to someone else's 4 paragraphs. Or maybe there arent enough people with anything thoughtful to say.
1. Publish your ideas early and often. 2. Have others debug your work. 3. Track the ongoing conversation around the idea. 4. Iterate.
That's how things should work, blogging in particular, but in practice people think differently about the medium. Many blogs are really bad, without commenters. But some people use blogging for what I'd consider essay writing.
Essays to me are about one person doing the thinking upfront and then publishing after they vetted it; the mistakes they make stay in their heads. In theory, an essay is could finish the issue at hand, but more often it doesn't. I think the best essays do close the issue they address.
I like essays -- I intend to write them myself -- but for a while I thought that they've become outmoded. Why let one person vet an idea in private, when it can be done publicly; it's much more efficient, when done right.
But there's still value in one person vetting they're own ideas before publishing. And some people are just better at creating "seeds" ideas to vet.
I like Greenspuns point about how mediums effect how people judge the veracity of an idea; I agree. There's certain ideas I don't bother posting because I don't believe anyone would believe it when expressed through a certain medium. Nobody would believe a new theory of quantum gravitation that first arrived as a forum post.
I'm checking my own blog sources. Very few people ever reach five pages, let alone twenty. Steve Yegge's penultimate post was 17 pages.