Let the touchscreen pause/menu button be available for everybody.

It's still forced ON on iOS, Symbian, and Meego Harmattan.

Not all touch devices have a back button or a hardware button to call up the pause menu (one example: Windows tablets that only have a Start button, which would bring up the start menu/screen, and not our pause menu), so it makes sense to let everyone turn it on or off at will (except iOS/Symbian/Meego Harmattan). Also, when the user is in-game, it cannot be turned off so that they can't get locked out by accident.