I'll say a thing, among others I could have told :
Being in our minds, art is fragile. So it has to be established on various supports, such a canvas.
But a canvas is fragile. So it has to be established on or with other supports, or with other functions : financial value, prestige, museums, decoration etc...
Perhaps that's something unevitable.
And that's why your post aim at separating what's art and what's only its various "supports".
@christower, thanks for commenting again! My post aims to art's function. What works of art are used for. I wouldn't call it a "support". Still, I think you get the point, when a painting (for example) is purchased and hang on a living room it may not stop being art, but that wasn't originally its purpose. Art is not meant to be useful.