Star trek missed somethings with thus tablet/pads. Each one seemed to only store 1 books worth of content. You can sometimes see people in the show using or handling a dozen tablets/pads. They seemed to miss that storage size would increase a lot.
You're pressuming the only cost is the price of the iPad. What about the luggage space each one takes up? What about the extra weight you have to carry? What about the mental processing of trying to remember what book/film/app/etc. is on which iPad? Why take 10 iPads on holidays when you can just take one?