Re: Cartels...
I think the difference is that the perception in New York is that you're not actually safer in a licensed taxi than you are in an unlicensed one; the cars don't seem to be well maintained, the drivers don't seem to be regulated. (It may not be true - I'm talking about perception). Hence, Uber is popular in New York - you can get cheaper fares.
Whereas in London (and presumably Amsterdam) the perception is that you definitely ARE safer - the taxis ARE well maintained; the drivers ARE regulated.
Personally, I would never use Uber.