In his very fine blog “Research as a Second Language,” Thomas explains why.

[Blogging] is not merely writing in another medium or even writing for another purpose. We might say that just as writing is not merely literacy, blogging is not merely literature. Blogging is an activity that is so distinct from the experience of writing that it should be called something else altogether. One does not write a blog post except in the sense that one “writes” a shopping list or a business plan. …

Some bloggers, of course, don’t know this. They try to blog by writing. They are perfectly competent writers and produce perfectly capable prose. But it is just not blogging. It remains writing. They are kidding themselves to think they have produced a blog post. They have written an essay and posted it to their blog. Others are, in fact, natural bloggers but kid themselves that their blogging makes them writers. Why should it matter whether you are submitting something to a publisher or magazine? Why does posting something directly to the internet undermine its status as “writing”?

… The short answer is that blogging is a social activity, while writing is, properly speaking, a use of one’s solitude. There is nothing solitary about blogging.