and added on an additional rider for her car from Liberty Mutual that covers "commerce" ... but it is/was not required.

Uber just asks if they have insurance.

I am guessing that "requiring" they sign up with Raiser is a recent development in response to getting hammered on this point. Does anyone know?

In fact, UberX -- sort of their high end service -- was started a year ago, at higher rates, to cover this concern but of course, most riders choose the lower end service.

But it does indeed sound like drivers have to have Rasier -- which is not Uber, but wholly owned by Uber. There is some question about whether that distinction protects Uber or not. It is understood that the intention is to shift at least some of the liability to the driver. As evidenced by the driver's terms of service.

http://www.sfbg.com/politics/2014/03/24/uber%E2%80%99s-secret-%E2%80%9Cproprietary%E2%80%9D-insurance-policy-leaked

What is most interesting is that the insured party is Rasier NOT Uber....