My blog had PR7 (Google Page Rank, now dropped to 5, but still) and I don't get many comments either, sometimes none for weeks. Some sites/blogs get tons of comments, some don't, I have no idea why, but if you care to research, that would be great. I'm sure the number of readers doesn't have to do with it. Posts of developer.yahoo.com blogs get a great number of visitors but not many comments, some posts don't get any.