While I agree with your first statement, the per-CPU analogy may not be right. The CPU (or car) is the resource being leveraged by the OS (or ride hailing service). Also, I may be wrong here but I think it's per motherboard.

For Uber to really become a monopoly would be hard, at best they could split the field with Lyft or others by making an under the table anti-"employee"-sharing agreement similar to the Apple-Google thing last year.