And who says an iPad or Chromebook has to be their main device?
For almost three years now Apple and others have touted the iPad and tablets in general as SUPPLEMENTAL devices, not primary replacements to a desktop or laptop. There are simply times and places where you can not use even a laptop due to time, space or power constraints. These are the times and places where a tablet or "thin client" have the advantage.
Desktops and laptops are tools; so are tablets and thin clients. Using the right tool for the job makes you much more efficient. Trying to force one tool to do another's job guarantees frustration and busted knuckles.