The fashion world has longtime been considered trivial and full of superficial people that only care about appearances. It's true that many people use and create fashion just to fix the exterior but this is not a unique feature of fashion. Appearances are everywhere, from the intellectual men or woman that writes or reads a complicated book just to show off his/her intelligence to the rich man/woman that buys a famous painting just to display his/her money.
For most of us it's difficult to see it but fashion is also a form of art. It's a form of expression and some designers like the recently deceased Alexander McQueen have used it to bring political or social topics to the publics attention. Fashion is also art because it's beauty too. It's colors, shapes, textures, materials, combinations, styles, feelings, points of view and craftsmanship like any other forms of fine arts. Fashion also takes your breath away when you see a masterfully crafted piece moving on the streets or in a museum. It also transmits emotions and feelings and has an effect on the observer as well as in the one wearing it. And maybe what Nigel says to Andy in “The devil wears Prada” is true: “What they (The designers) created was greater than art because you live your life in it ”