Someone correct me if I am wrong, but I thought that gyroscopes detect tilt/pitch/yaw and accellerometers detect, well, accelleration. The main controller will have both, as well has the external sensor bar to get position. (Accelleration can be used to get position, but the error adds up rather quickly.) So, this could mean that the nunchuk only has an accellerometer or that it has just as much position/tilt sensing as the revmote.
Still, this means that, in effect, revmote+nunchuk = controller with 3 analog sticks (revmote, nunchuk, nunchuk analog stick).