I've been thinking, and I wonder how many accelerometers are in the Wii remote. It could be that there's only one, and this thing could improve things simply by adding a second. For example, if you hold the Wii remote by one end and shake it back and forth, then hold it in the middle and do the same thing, the Wii can't tell the difference between the two motions. Both tell it you were moving the remote back and forth in a small arc. Add a second accelerometer, however, and suddenly that changes. The first motion is about the same, but the second causes the accelerometers to move in opposite directions. This increases the number of possible motions the Wii can detect, and should greatly improve accuracy for full arm motions such as swinging a bat.
If, on the other hand, the Wii remote already has more than one accelerometer in it, then I don't know what this is adding.