The point on shipping is appropriate... But just for clarity: of all the autonomous cars companies that ultimately "succeed", you will probably not be able to purchase cars from at least half of them. You'll only be able to purchase rides.
I know a lot of people at a lot of robotics companies (including autonomous cars companies), and have spoken at length with them about the ultimate business models.
Besides, it makes sense when you consider that most personal vehicles have sub-5% utilization. It's more capital and environmentally responsible to have shared assets rather than underutilizing assets with high embodied costs.