I think the change from drivers to driver less cars is a large enough one for people to accept and get used to, that it would make sense for uber to have their own small fleets of self driving cars in test cities, so that customers would get used to the self driving car concept in an environment where they could more directly provide feedback to the ones responsible for the car (uber in this case). It would also allow uber to work out issues that may arise from the change. I agree with others who say that this eventually leads to people having their own cars be taxis when not in use, I just consider the idea of uber managing their own small fleet a step towards that.