I just did a bit of research on the Wii remote system and while I am impressed at what it can do, it's doesn't appear to be a huge leap in technology over what the Top-Gun is doing. In fact, it looks like the Top-Gun is better in one sense in that the bars may be on the top and bottom or the sides, whereas apparently the Wii Remote "sensor bar" needs to be horizontal.
However, after playing with the Top-Gun for a couple of hours, I have come to a conclusion: The Top-Gun must use a low resolution CCD, probably 640x480 or smaller. This is based on the fact that it cannot provide single (or even double it seems) pixel precision. The Wii remote, according to reports, has a CCD that is 1152x864, or roughly 1 mega-pixel, which would be 3x finer.
Another difference is most likely going to be the scanning speed. The Wii remote (again, according to reports) scans at 200 frames per second. This will give opportunity for oversampling and averaging of the cursor position, making it more stable. The Top-Gun isn't bad for stability (worse for me when the bars were horizontal, BTW) but it certainly jitters more than the cursor I have seen on the videos of the Wii Remote in action.
The Wii still needs a bar that appears to be about 12" long either above, or below your screen. The system is no different than the Top-Gun in that if the bar is on top of a large screen, and you are pointing the camera at the bottom, the bar may be out of the view and the system will not work. So there are still the same type of restrictions with the Wii Remote as with the Top Gun. They may not be as severe due to to the fact that the Wii uses a slightly smaller bar and most likely a better optical arrangement, but it's still there. I have read that owners of projection screens needed to put the "sensor bar" in the center of the screen, or on a table in front of the screen in order for it to work.
There also seems to be no calibration for the Wii Remote, and have seen some complaints about it being "off" a bit in the menu systems. This isn't important in the Wii menu application because you are moving a cursor, much like a dot with a laser pointer. Light gun games require more accurate calibration, but this can be handled within individual titles, or in an eventual driver if used with a PC.
FWIW.
RandyT