isiscolo remarked that she wished people wouldn't link to the mode=reply? version of a post since she wanted to read the comments as well. Me too, I said to myself, the comments are part of the post.
It's a unique feature of LJ and blogs. In a mailing list or discussion board or usenet, people may quote your words and then write a response, which follows the original post or is threaded with it by subject line. The responses are generally of equal weight or importance to the original post and they are clearly their own documents.
But on LJ, the comments are attached to the original entry -- they are additions to it. It has one physical location. Unlike discussion board threads, the layout -- main post given priority, comments below clearly additions -- makes it one document.
So, the LJ entry is recontextualized by the comments. Its meaning may be enriched or changed or trivialized. When you comment on an entry, you are not creating your own document. Rather, you are participating in that entry, you are changing the way people may perceive the original words.
It's kind of cool.