To write for a magazine, they would have to establish the context, say something important, say it in a way that a wide variety of people can understand it, and then bring it to a close. That's more than most people want to invest.

But if you're reading somebody else's work, and you think, "Yeah, but there's another point," being able to drop in a paragraph that says, "Well, yeah, but there's actually this." There's an awful lot of counterpoint, the "Yeah, but..." kind of thought, on wiki. Discussion groups do the same thing, but with discussion groups it all gets lost.