That's one way of looking it. The other is: When a link is posted in HN to someone's blogs, why do people navigate back here to comment and not at the web page they were already at? I think there are some good reasons for that, including not wanting to be too critical in somebody's personal expression space, and also because at HN there is a commonly understood standard of discourse, whereas each blog has (or lacks) their own.

I agree about the commonly understood standards of discourse. With that in mind, it would be left up to the blog author to "opt in" by deciding to routinely grab their hacker news comments and integrate them into their own.

The comments are one of the best parts of HN and I think there must be few blogs that would want (and deserve) these discussions to be included with their original posts.