When designing websites and other "online" programs/activities, an important aspect is getting feedback from your audience. The reality TV-show American Idol is one example of how feedback is part of the show and if a bulk of that audience response would disappear, you don't have a show. The same goes for bulletin boards and communities--I've been "moderating" a few mailing lists but for the most part, they're dead because no one's posting or talking. Lately it's more of "not letting the spammers in" rather than "moderating and making sure everyone behaves".
Personally, I want feedback from my blog. If I had a choice of getting a thousand readers or ten new people who comments, I'd probably choose the latter because the former is more "invisible" than the latter. Whether you agree or disagree with what I have to say, it's nice to feel that I'm being read and I think the best way to express that is through feedback (unless of course you have totally nothing to add to the discussion).
That makes blogging, I think, very different from publishing. Because in publishing, there is no built-in feedback feature. Sure, readers can send in their letters or emails to the editor/publisher/author, but that takes some difficulty and there's no guarantee that your recipient will get your message. Moreover, it won't add anything new to the body of work--it's already written. Some blog entries, on the other hand, are valuable not just because of the main blog entry, but because of the discussion that ensues in the comments (and gives birth to future blog entries). The best model of this I think are message boards. Honestly, message boards are easily like group emails and banter between one person to another. An active message board writes themselves so to speak. Reading a book, on the other hand, is static. Each person might have their own unique interpretation on a body of work but they can't affect the book, can't challenge or change the text (that's what fan fic is for), and can't contribute to the discussion short of a new printing of the book (they might talk to the author about it but the author won't necessarily put the comments on display for the public to see--and will most likely use a different medium to do so, such as their personal website).
And in many ways, one of the best-written works is those that elicit feedback from us readers, irregardless if we agree or disagree on the topic. Which also makes designing an effective feedback application/program/activity not as simple.