The whole concept of "tree-ness" is an interesting one. Most all of my bonsai fall into that catagory. I think most bonsai growers would agree that bonsai
should look like a tree. That's OK with me. I once had a client ask me "what kind of tree is that bush?" Which was kind of funny because I was planting a witchazel at the time he asked me.
It can be classified as both.
It's really a matter of words, definitions and your individual point of view anyways.
Craig is right on when he says " the meaning of bonsai has changed through the years." It will most likely continue to do so
as time goes by, but I doubt if the same definition will satisfy every individual grower.
In the end, I don't think we can define with absolute certainty, any of the Arts. I do believe Bonsai is an Art.