Despite their advertising to the contrary, Uber's rates are not always lower than yellow medallion cabs in NYC. For certain trips it may be cheaper, but oftentimes it is just as expensive, if not more[0].
Uber's pricing structure is different from the ones that the medallion cabs use[1], so it's not a one-to-one comparison. This makes it very easy to pick and choose certain trips which would make Uber look cheaper (which they do), and it's also easy to pick and choose trips which make them look more expensive.
In addition, Uber is venture-funded and can easily operate below-cost right now (I would be shocked if they did otherwise).
So it's worth keeping in mind that Uber's rates are arguably already be no better than taxis', depending on the city, depending on the trip, and especially if we assume they had to operate in the black.
[0] This is hard to verify as Uber explicitly prohibits using their API for price comparison, specifically to discourage this. Though there was a project on HN a few weeks back which did do this, and the results were mixed (Uber won sometimes, but not always).
[1] Which are set by the government, not by individual cabbies: http://www.dailydot.com/technology/uber-nyc-taxi-cheaper-pri...