Thanks that could explain it. I didn't ask his sons disability as it was none of my business and being disabled myself I know some disabled people don't want to discuss it unless they broach the subject first. I used one on space mountain (he gave me 12!!!!) and have the rest in my waist bag still. Reading your explanation makes me feel guilty about using the remaining ones now as they were probably issued for reasons other than 'bad legs'. I'll probably ditch the rest to be honest.
12 seems like an awfully high number. I was hearing 2-3 even if you were there multiple days.
My wife read about them from a blogger who had been given a tour of the system the first day, she made it sound like this would be standard, but we were not offered, nor did we demand any as we wanted to try the system as it was designed.