It's forced deregulation by circumventing the rules.
One interesting argument is that deregulation increases the supply of drivers hence making them inefficient. As they are inefficient the prices increase. Interesting POV.
However given that the American Medallion system doesn't seem to be working, there aren't enough drivers and a medallion is worth so much, screw that theory.
http://www.bloomberg.com/news/2011-08-31/ny-cab-medallions-w...
http://en.wikipedia.org/wiki/Taxicab#Regulation
Uber have hit a nice niche in America where they're taking advantage of over regulation. And the really odd thing is the cities saying Uber is A-OK, they're just idiots. They should deregulate instead of making a special Uber clause, it's bad government. But that's the way it works I guess, the ludicrousness of local politics around the world always makes me sad.
Note that their success isn't really anything about customer obsession, the only reason for their success is because of regulation. You wonder whether that's a happy accident or the entire private car thing is a cover and they're deviously cunning. All respect either way.
Speaking from a country without these sort of onerous regulation where a taxi is a trivial and cheap thing to get in minutes, any city getting rid of the medallions will put uber out of business practically over night.
The problem they'll face is that as grow they will probably put themselves out of business by encouraging mass deregulation, and then they'll be expensive with no value add. Their customer base will dwindle as new customers won't want to pay the premium for a chauffeured car and that'll be the end of it. Probably a good 5-10 years away yet though.