That is just game design, it has nothing to do with the input medium. If a game is designed to sway with no input then it will sway weather the wii mote is giving no input or the mouse is giving no input. If you played the same game with both the wii mote wouldn't have any inherent advantage.

The fact that sway in a mouse is so minuscule that it has to be added artificially tells you how stable a control scheme it is.