A gyroscope just resists rotation.  You can measure that resistance to calculate how much rotation has happened.  MotionPlus includes a multi-axis gyroscope so the orientation of the Wii remote on each axis can be tracked in terms of change from a previously known orientation, a.k.a. home position.  Combine that with the existing accelerometer, and you can see a dramatic improvement in waggle-ometry, but you still won't have the mythical "exact position in space" we all thought Nintendo was talking about back in '05.