I think Steven’s point was more that comments shouldn’t be thought of as copyrighted content, and that they should function more like a conversation in a bar or on a street corner — and I would agree. Legally though, I’m pretty sure they would be considered published content, and are therefore “owned” by their creator, unless he or she gives up that right to the blog or service that hosts them. So could Robert Scoble sue Rob La Gesse for deleting his from FriendFeed?
Michael Beck points out (on FriendFeed) that these questions have come up before, and points to a discussion here, and also here and here. Meanwhile, Daniel Ha of Disqus — the comment aggregation system I use here — has drawn up a prototype for a “commenters’ bill of rights.”