I don’t have a very good answer to your direct question but I can give you somethings I do know. There are always those people in the world that are good at everything, you probably know people like that. Think of a valedictorian or MENSA members that scores the 200 on an I.Q. test. The thing is that they are good at everything but they aren’t the best at anything. Some people, handicapped or not, focus their skills on one certain thing that they love rather than spread their focus on a multiple array of things. An example that comes to mind is having money to spend on a car, you could spend it all on the engine or you could enhance the overall ability of the car by spending some money on shocks and tired and breaks ect.
It isn’t my place to claim this because I am not handicapped in that way and I hope nobody takes offense but maybe those people can’t focus on multiple things like others can. The one thing that they really focus on causes them to lose themselves in their passion.