The bindings and skis themselves aren't foot specific per se. I'm not sure if someone has already touched on the reason in this thread, but it mostly has to do with boot wear. Most people have an irregular gait, i.e. their left foot and right foot may follow a slightly different path during your normal walk. A lot of this has to do with possible past injuries, such as ankle, knee, or hip injuries, and some has to do with slight anatomical differences that occur naturally (one leg longer than the other, scoliosis, etc, bowlegged, knock-kneed, etc).
Basically, due to these differences in your legs, one boot may eventually develop a different wear pattern in the lugs that interface with your bindings. Over the life of your boots, these differences may become pronounced enough to where it may affect the release of your bindings. Hence, when your bindings' release settings are checked by techs, they test your individual boot (left and right) to the corresponding binding.
Normally, these differences are minor and won't cause any problems. If you've got a genuine concern, mark each binding themselves with a permanent marker. With stickers losing their adhesive, especially considering that skiing is a sport that takes plance in damp conditions, marking the bindings themselves is probably the way to go.