When the economy goes south, so do hemlines, according to the highly disputed theory first perpetuated in the 1920s. What isn’t in dispute is that today, the relationship between the economy and the fashion industry has become a bit more complicated than skirt lengths. Behind the flawless frocks streaming down the runway at New York’s recent Fashion Week (featuring skirts, incidentally, that reached for the floor) is an industry in the throes of some sweeping fundamental shifts.