Yeah, its not so much the scaring issue as the conditioning aspect, LOL!!
Its the same as working your horse too consistantly on one side, then when you go to do the same on the opposite you don't get the same response you had hoped for when you had been working the original side!
I heard the same about cell phones.. Never had an issue there, but of course I forget mine all the time and lose it alot too!
When I was working with Ember prior to her first show, I learned quickly at the show that horses pick up on the darnedest things to cue into. Usually I wore my casual work attire when training her.. Then on show day she started pinning her ears at me (which was not only unacceptable, but very unusual). It wasnt until later that day when I removed my hat, that her ears came up.. Duh!! She didnt like the cowboy hat!! I felt like a tard when it finally dawned on me! Funny thing is that she still doesnt care for me wearing it. One sunny day I brought it out and wore it to help with all the shine. She listened to what I asked, but was a little more resistant in her demeanor. I was still able to get her to do what I wanted, but I didnt care for the attitude even though it had no effect, LOL!