Apparently, reader comment feature is not popular among bloggers. Some evidences:

1. While Radio supports it, many radio themes don't even show it.
2. Most of blogs I visit don't use it.
3. If used, I hardly see any comments.

I think there are two factors that discourage blog comments:

Etiquette - Unlike discussion forums like slashdot that convey the feeling of a public place or neutral ground, blogs are a part of someone's home page and convey the feeling of someone's home.  So posting negative comments on someone's blog is like saying something bad to a party host.

Visibility - Blog comments are typically not displayed inline of a blog.  Only indication I see is "comments [0]" after each blog post.  Out of site, out of mind applies here.  Also, "comments [0]" reads like an empty restaurant, not too inviting.

The reason I am poking into blog features is to identity the ingredients behind blog's popularity that I can apply in my groupware projects.