"Is there a particular reason the manual and the tools have to be a flight of stairs away from the technician? I'd wager that the comparison would lose some steam if the tech could just turn his head to the right."

I've never worked on planes, but quite a bit on cars and semi-trucks. You can get yourself into some tight spots. There may not be room to bring a manual with you, let alone turn your head to look at it. The closest I've had to glasses is bringing a smartphone to look at a manual or photos - but having it right on your had and hands free would be a huge help.