Comments are a way of verifying that someone is reading. They are social contact. I think all bloggers look for content. I read a dozen or so blogs a day and regularly comment on 3 or 4. Hence I am a lurker on more then I am a social interactor. I think the 5 or 10 to 1 ratio of readers to comments would hold true. The heavier the traffic, likely the more lurkers.
Comment can have issues. I leave my blog open to all, and occasionally have to delete a nutter with a message unrelated to the blog. Some review and approve comments. Some get into arguments with commentors (and sometimes delete their blog in a huff.) Sometimes the software makes posting comments difficult. I had one recently that didn't post, I waited and recommented, the next morning three comments appeared. Oh well.
I blog because I want to. I love comments as they verify that someone is reading. I appreciate the social interaction. I will keep rambling, please keep commenting.