I have been wondering on the same thing. 90% of people using the desktop or Laptop now are basically the same as they are doing on phone. Social Media, Youtube, Web Surfing etc. Even some heavy lifting like Video Editing can be done on a Phone. In terms of computational power, if you add two more Core ( Our current Desktop CPU gets 4 thread from 2 Core ), and double the memory, there is nothing much left apart from the UI difference.

How far are we from that? 2 - 3 years? Where will iPad fit into it?