We have just got back from the Norwegian Jewel and have noticed a couple of guests were on wheelchair. In fact, our room were designed for people with wheelchair as we asked for a bigger size room. Everything inside were catered for this purpose. For example, there were a lever in a wardrobe so you can pull the lever down to hang the clothes so you can do so as sitting on a w/chair.
On Norwegian Dream for Baltic cruise, my wife is in a wheelchair and had to go to cabin for toilet as no wheelchair accessible toilets elsewhere on boar.