Lou, before I drove I took Uber to the airport with my friend who said we didn't need to tip, it felt extremely odd not to give this guy a few bucks, it really did, I can't emphasize that enough. Most parts of the service industry have tips as part of the equation, most know that the minimum wage is not going to cut it. As a restaurant manager I would advise diners if they really pressed the matter that part of the reason you visit is because you presumably know the service is excellent, for that to continue the staff have to be rewarded appropriately according to the industry standards, they pay a percentage of the total bill, if they don't get tips on a regular basis they will be working for your pleasure only!
Uber riders know what they are doing and know how they feel about it, pretty cheap, just to correct a little ambiguity or misinformation is not going to make me feel bad if it becomes widely known that no tip equals 3 or 4 star rating, we are not kidding anybody here, they know as they step out of the car, they know we know, there should be a minor penalty for conveniently avoiding what is obvious when its at the expense of another.