Surprised; I thought Uber was some sort of public-access ridesharing thing. If they vet drivers and license them, how is it different from any other cab service?

Mainly because they don't actually license them unless the local authorities force them to. They do vet them, in theory.

And to follow-on, the practical difference is that they are a lot less terrible than most existing cab / car services.

People have been selling/giving away their Uber accounts too, IIRC.