It's Carnival's policy also Sonny. Yes, they will let you book it, but if needed by a handicapped person they will move you. But as Sonny said, most likely to a better room anyway. Also, it can depend on the timing. Sometimes if you are booking way in advance they won't let you book the handicapped accessible cabins. (Assuming that they will need them) Whereas when the cruise date gets closer and a HC person has not booked that cabin they will open up booking to anyone.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise, Magic 1/14
NCL Dream October 2006, RCCL Mariner OTS June 2007, Celebrity Silhouette 2013