I'm not sure what stops EasyTaxi from working in the U.S. I use it in South/Central America and it routes regular taxis, you pay in cash like usual but get the convenience of the Uber experience of knowing a cab is on the way, and who the driver is.
At a guess, it's because it's a Rocket Internet company and the group generally does not like operating in the US for a variety of reasons (chief amongst which is that their business model is to execute ideas in emerging markets, not developed countries).
There are. But, they are inherently limited. Via fixed supply and fixed pricing.
Exactly what is Limited by supply and price? Surely not the app? Perhaps the dispatcher charges a fee for access to the API?
The cabs themselves. There are a limited number of licensed cabs, and prices are preset.
I don't see how that would negate the convenience of an app.
You need a variable supply to accomodate for varying demand. Uber would not be able to deliver 10min and under pickups if their supply was limited.
NYC is a special case - yellow cabs are not allowed to be prebooked in any way, shape or form. Street hails only.
(they're piloting an e-hail scheme, but it's far from done)