Mostly I agree, these devices good for books and reading / watching static web content.

But regarding gaming, it depends. For example, the Pinball Arcade is very good on a tablet and one of the few reasons to own one .

Productivity wise Windows tablets would be better but if you play a game like Pinball Arcade on Windows with tablet hardware such as the budget Asus T100 and its energy efficient but otherwise slow processor, you feel the graphics hardware is lacking to run a full blown windows game, even on directx9.
On the Android platform the graphics and controls have been adjusted for optimal usage with the weak hardware and touch screen input respectively.

Also, make sure that you purchase a tablet with a display which allows to dim the backlight low enough to be able to read in low light without too much eye strain!