Discussing the pro's and cons of our tipping culture is a totally different topic up for debate and here is probably not the right place to discuss it further. However, within the norms of the tipping culture many live in today, it is customary to tip most private drivers (non-public transportation drivers). The tip shouldn't change based on some means testing of the person receiving the tip but rather it should be based on the level service you received and what the individual giving the tip feels they can afford and\or the person deserves.
It would be no different of someone called a restaurant that offered free pickup. Yes the service is free and the driver is probably still getting paid for the ride but most people would still tip the driver....and then the waitress. Some would tip the driver even more then they would if they had hired the driver, irregardless of the driver collecting a fee from the restaurant, simply because they recognize the value of a free ride.
