I think that the clear point is simply that blogging is not a subset of journalistic writing — journalists may blog, and their training and professional creed may obligate them to apply (semi) strict journalistic practices to their writing. But blogging’s scope is wider than that: it’s simply a medium, and it’s a plastic one.
One can imagine a blog that simply documents — warts, confusion, and all — one’s process of exploration. It might surprise the general public to see all of the searching and randomness that is involved in using sweat and intuition to reach out past the known facts. A science journalist would probably not write such a blog — but perhaps one should: about the process of writing and coming to terms with what they learn and craft as they go about absorbing and summarizing.