At least the article explains what motionplus is correctly:
"This can be solved with the addition of a second accelerometer, ideally at the other end of the remote, and that is what the MotionPlus appears to be. With less sensitivity, but no 3G limit, it becomes possible to track the location of the remote with much greater accuracy, as reported by those who've had a chance to play with the sensor."
The existing Wii-mote has the sensitivity, its the removal of an upper G limit for the "MotionPlus" that helps them keep full track of location. Also you can use the second set of data to normalize the overall motion data and remove noise motions.








