IGN claim to have found final secret in the Wii control: A speaker in the control, not exactly big news...
Edit: Just noticed a hardware section, sorry! Please moveNintendo today unveiled the final piece in the Wii controller puzzle: a built-in speaker placed in the middle of the freehand-style pointer.
The square audio outlet is used to deliver "in-your-hand" aural immersion. Since the right-hand Wii-mote is used for direct interaction with objects in the games, Nintendo included the controller speaker to give players direct audio feedback pertaining to do those objects.
For example, when you are casting your lure while fishing in The Legend of Zelda: Twilight Princess, you can hear the whirring of the line as you flick the controller forward. Likewise, when you nock your arrow and pull back the bow string in the game, you can actually hear the creaking and more accurately feel the tension on the string.