Most blogs fall into two categories : 1) hugely popular with mass readership; these tend to be bombarded with absolutely retarded comments from the general internet community, and the comments often turn into flame wars between various readers and are just generally useless; 2) intimate, read mainly by friends.
This latter one is a little weird. If the comments are public, or even if they're friend-only and you're one of the friends, you get to read the very personal notes that are left between friends. This has an addictive appeal - blogs in general are largely interesting as voyeurism, and seeing intimate friends' comments about posts just makes you feel even more like you are getting a sneak peak into someone's life. It's weird to me that people act almost as if this isn't happening. Most people who write comments on blogs write little notes directly to the author. Why don't they just email the author directly if it's a personal note? Why don't you write as if your audience is the anonymous internet reader? (a similarly bizarre phenomenon exists with the Yelp Compliments, which are public, and yet people shamelessly send desperate pickup attempts to girls through the compliments, and the girls go ahead and approve them for public viewing; I don't get it).
So I think I like things the way they are. I like getting into email conversations with readers. When people send me things that are corrections or useful extra info, I often post it back here if I think it is interesting and appropriate for the general readership.