Well John, your video was spot on for demonstrating this most basic 3 rail principle. It's perfect for beginners.
One small bone to pick though: your nomenclature of "dead rail" and "trick" is a bit off. The correct term is "insulated rail", and it's not really a trick as it has been well documented by Lionel for over 75 years. Perhaps a better word would be advantage or phenomenon.
One important point that you failed to mention is the type of track that you used for this demonstration. As far as I know, there are only two brands of track on the market that naturally lend themselves to doing this. They are GarGraves and Atlas (edit: oops I forgot Ross). All other brands have their outside rails tied together electrically, and require special measures to insulate them so they can be used for this purpose.
On a personal note, my railroad relies heavily on this principle, though not for activating devices, but rather for detecting where trains are along the mainline. Wires from all the insulated track segments are run back to a panel, where the occupancy values are sent to a computer which returns signal settings to the layout.
The insulated rail is a very powerful tool, and should be taken advantage of whenever possible.
