But at its core, Uber is a black-market taxi service (unlicensed vendor operating in a regulated market). Just like cigarettes and alcohol are cheaper in the black market where vendors don't pay taxes, one would expect Uber to be cheaper than the taxis that have to pay medallion fees and meet licensing regs. Cheaper doesn't mean right. If you like Uber, lobby to change taxi cab regulations (and I think you may find that while there may be room for improvement in their implementation, there are reasons for taxi cab regulations).
Here in New York all Uber drivers are registered with the Taxi & Limousine Commission and have to meet city requirement re: licensing and insurance. I'm sure Uber would be happy to comply with the regulations that cities eventually come up with as long as those regulations are focused more on protecting consumers and less on protecting the old taxi industry.
Uber Black perhaps, but not UberX, which is by far the focus of Uber now. Around here Uber specifically advertises UberX as a taxi, and openly does price comparisons between it and taxi fares (as opposed to price comparisons against other limo services).
Let's also not forget that Uber started as Ubercab and was forced to change their name. I don't think they ever intended to be a limo service, and their current product offerings are largely not limo services.