The zapper on the NES was great as was the scope on the SNES, making a gun attachment on the Wii I think is pretty useless, the accuracy just isn't there so will never be good enough to use as a gun on the shooting games, you still have the crosshair on the screen which doesn't even line up with the end of the Wiimote anyway.
The idea of guns is to do away with the crosshair and have the player in full control of the aim.