The point you make about seperating controls with seperate functions is an interesting one, but becomes hazy in the realm of aircraft control. In an aircraft, the simple 'single' intent to execute a level turn requires control inputs from elevator, rudder, and ailerons, every time, no exceptions, if you want your turn to be coordinated and aerodynamically efficient. So thinking of these controls as being 'separate' because they control separate surfaces on the aircraft doesn't quite fit. When I take people flying in my little two seater taildragger, novices are always amazed that a simple turn requires the application of three coordinated control inputs.
Very true for real aircraft -- not very true for models, which can be flown with only two primary controls -- particularly with the average RC Trainer (powered or otherwise). Of course, the need for coordination returns by the time you learn to fly more advanced models, but by that time the novice has usually developed the stick skills needed to handle the more advanced controls (or can cheat with a computer radio ...).
