Uber like Airbnb is leveraging individuals capital (or ability of drivers to go into debt). However unlike ground in prime location they are literally stamping out new cars every minute. In case of self driving cars it is Uber putting up the capital and margins in transportation fleet business are smaller than what the current Uber valuation implies. Differentiation will be difficult.
It is a risky strategy for Uber but it is hard to see an alternative for them.