I assume the lights on the bar makes a reference, who the sensor in the hand held inteprets as distance, angle, and position.
The result, i assume, is its using a "virtual tv" box, who is projected who makes for a good game experience.
Lets assume now, the viimote had a TV camera thingy in it, and the VII had cpu capacity of actually acting as a light gun. What would the advantage be?
1. you would get good control at close range, and, less subtle control at large range. With a set "box", you can aim on feeling, and have better control.
More, i also guess, game devs can code a adjustment in the game, a simple one, who adjusts the response before game starts. If its felt needed.