It's an interesting observation. I agree that I'd love to spur more discussion on content, because often the comments are more interesting than the content itself. I have found that adding a bit of text with a link increases the chance that people will comment on the content. Typically we post things that we find interesting, so it doesn't seem much to ask that we comment on why we posted it. Maybe after adding a url, you should be prompted by the question: "Why did you post this?" I do believe that overuse of the moderation tools can have a stifling effect. But there may be other ways to encourage comments without changing moderation. I am open to any suggestions. We could add the 'shared by' number and link as seen in chatter to all comments. We've previously considered it.It would be interesting to know the number of shares vs. the number of views for a post?