The Internet possesses and endless and continual discussion about a million topics.
A blog post is the author's prompt to gain focus in the ongoing (and evergoing) discussion to a particular topic, and relative to the author's given position.
It's like a button sewn into the conversation fabric. It's also part of the fabric and it has a little more gravity than a comment thread.
I should clarify. It's more that the old newspaper/publication opt-ed mindset where a columnist writes a piece that goes out to readers in a one-way form of communicating that doesn’t facilitate responses easily, has given way to a more open exchange of thoughts between reader and/or author. It’s his blog and his rules of course, but I don't see the value in discouraging a full-on discussion that may arise out of something compelling which someone wrote. I’d like to think that’s one of the great things about blogging, in that it democratizes the development and sharing of ideas.