I think in the past it was necessary to have doctor's prescription to get a wheelchair/EVC. Now with rental agencies out there, if a guest has problems walking or standing for very long, they get a EVC. That way they can enjoy the parks with their family and friends.
Also if it was your relative that needed to use an EVC you might be thankful that Disney has such a service. I too get impatient with the delays, but try to remind myself that but for the grace of God that might be one of us.
I think there is discussion about this matter is on the handicapped boards here on the DIS and since this subject is not really
DVC related, the moderator will probably close this thread.