I agree that those are reasons for the INTENT behind regulating/licensing taxis. Certainly in the past those things may have been more important. However, with the improved access to information that people now have through their phones it seems a lot less necessary.

- to keep traffic down I don't know if limiting taxis actually ends up limiting cars, but limiting cars is certainly the definition of keeping traffic down. - to ensure a minimum standard of vehicle I've actually been surprised but the people driving Uber X usually have nicer vehicles than most taxis I have taken. - to ensure safe, well-trained and responsible taxi drivers. Licensing drivers provides responsible taxi drivers? Yes, tell that to the people that have to pay cash because the credit card machine is 'broken'. - to ensure a fair level of income As far as the fair level of income, taxi companies are taking their cut. How much do the drivers actually end up with?