The practice of tipping or not and how much is in a large part cultural, of course. I was just answering your question regarding the case of taxis specifically, since (in NYC, at least) I think the circumstances of "taxi economics" put most drivers at a disadvantage, and I try to acknowledge that by tipping.

I don't know if in Europe taxi drivers are better paid or have more autonomy, but I wouldn't be surprised. This article has a lot more detail on the issues with the medallion system: http://www.slate.com/articles/business/moneybox/2012/06/taxi...