At Confessions of an Idiosyncratic Mind, Sarah Weinman gives a great entry about why blogs are different than journalism and what keeps us reading. Here's one portion:
"Second, the best blogs know how to construct their content to keep reading. Just when you think they've put up a fantastic post--oh wait! Here's another one. Just when you think that earlier post couldn't get more thoughtful, provoking, or controversial, they are back with another one. Blogs know how to move quickly, efficiently, and keep the reader strung along."