Sure, starting a real conversation will always be left to the writer. But there have been plenty of times when I've wanted to contribute something but couldn't

Sure, starting a real conversation will always be left to the writer. But there have been plenty of times when I've wanted to contribute something but couldn't be bothered because I'd have to return to site for the next few days to check for replies. While I may do that on HN (like right now) I won't normally do that for Joe Random Blog.