Oh yes, I suppose the poor guy just loves having to take a spare pair of false legs with him.
Where somebody is clearly disabled, or has a chronic illness, anything they need should be free of charge, as long as it is of reasonable size and they have a doctor's letter.
Incidently, Jet2 are the only airline I know of who charge for dialysis machines in the hold. FR and BE not only don't charge for the machine, but allow an additional free allowance for the sundry equipment that takes up space in the passenger's other baggage.
But then perhaps you feel such people shouldn't be allowed to have overseas holidays?