OK, think of it this way... No matter what kind of controls you use, all the different controls have to be covered in one way or another. Now, knowing this, how do you replace the motion with the gamecube controller? You can't, there aren't enough joysticks on the GCN controller. There are also buttons on the GCN controller that aren't on the Wii controller. The game would have to be designed to use one or the other. Either that or have an option to switch (which you can't expect every game to have).