(Left as a comment on a yet another thread about "what is a blog?")
A sheet of paper, a pencil. What is scribbled on that piece of paper (and arguably the role the person doing the scribbling takes on and gives his/her scribbles, and how the reader perceives it as well) is what makes it either a poem, a diary entry, a novel or a "news story"...
We don't call all those things "paper" do we? We don't argue over whether the gossip column is journalism do we?
So now our paper and pencils are freed from their earthly atoms, and we have all these linking and annotation features. "What it is" is what it is... quibbling over (most of the) details serves little or no purpose. Let's use our time and energy figuring out all the wonderful things we can DO with it.