That's not entirely true. There has recently been a number of changes to the ADA regarding hotel reservations:
(e)(1) Reservations made by places of lodging. A public accommodation that owns, leases (or leases to), or operates a place of lodging shall, with respect to reservations made by telephone, in-person, or through a third party --
(i) Modify its policies, practices, or procedures to ensure that individuals with disabilities can make reservations for accessible guest rooms during the same hours and in the same manner as individuals who do not need accessible rooms;
(ii) Identify and describe accessible features in the hotels and guest rooms offered through its reservations service in enough detail to reasonably permit individuals with disabilities to assess independently whether a given hotel or guest room meets his or her accessibility needs;
(iii) Ensure that accessible guest rooms are held for use by individuals with disabilities until all other guest rooms of that type have been rented and the accessible room requested is the only remaining room of that type;
(iv) Reserve, upon request, accessible guest rooms or specific types of guest rooms and ensure that the guest rooms requested are blocked and removed from all reservations systems; and
(v) Guarantee that the specific accessible guest room reserved through its reservations service is held for the reserving customer, regardless of whether a specific room is held in response to reservations made by others.
So yes, Disney is not required to provide a ground floor room if someone requests it, but if the guest specifically reserves an accessible room, then Disney is required to hold that room for that guest.