It's all simply a matter of taste, experience and/or opinion when you get right down to it. It's like trying to define clam chowder (is it made with milk or tomato?) or chili (beans or no beans?). It's all good and we can take it as far as we want to in any direction we like.
I've seen some absolutely beautiful paper quilts...three layers intricately stitched together with threads...and paper is, after all, plant fibers, just like cotton. Some things in this life defy definition...quilts may just be one of them. :D