They basically mean the same thing - describing what is in style and popular. 'Vogue' is given as a synonym for 'fashion'. There is a slight difference in flavor. 'Vogue' gets used more when refering to something snobbish and shallow. An idea that is in vogue usually gives the picture of an idea that has no real basis in fact, but is popular anyway just because some people think that other people are thinking that way and so they must. "The idea that you could tell a persons personality by the shape of their face was in vogue during the 1800's"

Vogue: noun 1. something in fashion, as at a particular time: Short hairdos were the vogue in the twenties. 2. popular currency, acceptance, or favor; popularity: The book is having a great vogue. Fashion: noun 1. a prevailing custom or style of dress, etiquette, socializing, etc.: the latest fashion in dresses. 2. conventional usage in dress, manners, etc., especially of polite society, or conformity to it: the dictates of fashion; to be out of fashion. 3. manner; way; mode: in a warlike fashion.