Like some others have mentioned, the title is somewhat misleading. There is no feasible way that Google ends up owning the entire market. And I'm not talking about the actual cars, because they're definitely not getting in the car making business. Even when it comes to the software, they could only be the only provider in the market if it becomes a government regulated monopoly.

As a side note, I think the resistance to driverless cars will be a big psychological stumbling block. I can't ride in the passenger seat of a car without hitting the "brakes" and pressing my foot into the floor. It will be tough to break habits and to trust that the software is safe.