gzt: The simple answer is that Uber is not a ride sharing service. The driver and passenger do not share the same destination or purpose.
I think the ride sharing concept comes into play because you can be sharing with other customers. I'm not sure if that fits the legal definition of a ride sharing service in New Zealand, but that's definitely how their low cost option operates overseas (once again, no comment on whether this is legally so). We had a few Uber rides in San Francisco that we shared with other passengers.