It's a legitimate. People have used car wax on their car windows for years to help keep bugs off and prevent scratching. It works to a certain extent. Those who wash and wax the glass don't get that strange pattern where the windsheild wiper is.
However as was said above, it's not practical on the screen.
Also realize that wax isn't really much protection at all. It's just with cars you have little choice. Wax in theory creates a one atom thick coating and possible thicker in the little microscopic grooves and craters. It helps but not much and doesn't really last very long either. On a touch screen it would come off immediately. That's not even getting into the different types of wax. An abrasive wax cleans but would also damage soft plastic. A non-abrasive polish probably just wouldn't stick.
the best way to protect the screen is to keep it clean and use a rubber tipped stylus.