"Was the left-wing blogosphere always mainly about Iraq?... Maybe the whole blogosphere was about Iraq!"
Traffic problems — noted by Mickey Kaus.
Hitting a blog is an emotional expression, and some blogs attract readers by being the place it feels good to hit when you are charged up about something that is happening in the world. A mutually dependent relationship develops as the blog must satisfy your emotional needs without curing the distress that made you hit it in the first place.
ADDED: Actually, the Kos traffic looks like a pretty stable plateau to me.