In the juiciest speech in “ The Devil Wears Prada ,” Miranda Priestly, the frosty-haired, frosty-souled Runway magazine editrix played by Meryl Streep (in a performance that should have won her the Oscar), looks over Andy ( Anne Hathaway ), her dressed-down second assistant, and dresses her down all the more by explaining that Andy may think she has nothing to do with the fashion world, but she couldn’t be more wrong. Using Andy’s lumpy cerulean blue sweater to illustrate the point, Miranda explains how fashion filters down into the world in a thousand ways no one realizes, and that we all obey its dictates.…