A customer signup requires a valid credit card, so riders are identified. Signing up as an Uber driver requires proof of vehicle insurance, registration, inspection, and a background check.
A cabbie or livery driver can signup, but they will be a known entity. Plus with every ride Uber provides for a driver rating and offers a feedback if there is a problem.
Because documents and credentials have never been faked. Ever. And some stupid app is on top of it. Got it.
What do the insurance companies say about using your personal vehicle as a business? I have wondered about this since I first heard of Uber.