You are assuming Uber would want to own the cars. Probably they would want to let the car owner put it to work, while it would otherwise be sitting in the garage or parking lot.
Totally agree - the Otto purchase suggests that they're looking to retrofit existing cars. I'm guessing this means you still need that driver network to at least provide the vehicles (and potentially manpower in the short run to ensure safety).
So let me get this straight. I'm a private citizen early adopter who buys a fancy new expensive self driving car. I'm super fond of it because it's a hot new technology. Then I lend it out to Uber to have the shit beat out of it with city driving, drunk people puking in the back of it, etc. And I'm supposed to cover the costs of maintenance and cleaning. Uber better be offering me a fuck load of money, otherwise that sounds like a pretty bad deal.