2a) HN wants people to link to the original source article. So, in theory, blogs would not get posted.

2b) HN asks people not to editorialise when submitting links. Thus, if you want to include some text about an article you're submitting you're supposed to make a blog post, with a link to the article in the blog, and then post to HN the link to your blog post.

At least, that's how I understand it. It feels sub-optimal.