Very true but most people in wheelchairs do gain weight. Some people gain a lot of weight. I can not begin to tell you the number of less then pleasant rear views I have seen while fitting wheelchairs.
It mostly depends on the persons health and medical condition. Then if they are able, the desire they have to stay in shape.
Exactly, people have the chance to make the best or worst of a situation. Not many medical conditions FORCE someone to become obese.