@DeanClark Lived here for years. An across-the-board increase is completely different from an incentive that is conditioned on showing up and building a good reputation. An across-the-board increase has no such incentive.
@ninetysouth Clearly it's the incentive for cab drivers to use the system. By earning more than your average street fare, it gives them a reason to adopt the app, honor pickup requests and build a good reputation. Riders pay more, but in return they get easier, reliable pickups.
Other taxi apps have had all this except for the gratuity part. And they all suffer from poor adoption because there's not as much in it for the drivers vs. the current system.
You could think of it as a "surcharge" if it's easier, although Uber is likely positioning it as "gratuity" to steer clear of pricing regulations.