That is certainly the thesis behind the wild valuation of Uber - but so far Uber hasn't really shown the ability to lock customers into its taxi network. Whoever develops the self driving cars can build the Uber app/network part of the system much more easily than Uber will be able to build the self driving car part of the system.
It's not clear how you could lock someone into a taxi network - by definition, each taxi journey is a separate purchase, unaffected by previous decisions (once you've installed the app in the first place).
Prepay discount mentioned above is about the only legitimate possibility. There are plenty of not-so-legitimate possibilities (see the Uber vs Lyft poaching discussion)
