Also, a risk here is that other large parties will make the same calculation, flood the market (anybody with money will be able to start a cab company with a lot less hassle from labor laws because you don't need that much personnel) and drive margins down.
To win in this space you probably will need both a lean model of operations and a good image in the customer's eye. Uber currently seems to have both, but committing _now_ to a provider of cars is risky (what if other manufacturers turn out to have better or cheaper self-driving cars?). On the other hand, it also may be necessary to commit now in order to stay lean (committing now probably gets them a nice price cut)