UberX drivers are also paid as contractors, so there is no withholding on their paycheck and they must make up the difference themselves. Does anybody know if this is the case for regular cabbies?
In many places, drivers are independent contractors, and most of what the company does for them is deal with the equipment, vehicle insurance and the licensing. Pretty much everything else is the cabbie's responsibility.
That said, regulations are different everywhere, so while this is probably the most common arrangement in the US, other setups are not necessarily illegal.