usually micro controllers are preferred over micro processors  this is usually just to minimize the cost and the application usually is designed to perform a single ended fixed work lets say a air conditioner which has a microcontroller for controlling the temperature ,swing of air  ... so this  is a small end application which does not require a heavy processing . But   in today scenario the companies  are focusing on high end controller with heavy processing the most common example is your android based mobile which has ARM based processors