NYC cabbies complained about having to accept credit cards, but with a fair bit of data now available, it looks like it has contributed to an increase in ridership. (I did a quick NYTimes search but could not come up with the article.)

As to the suggested tip, I'd be surprised if the driver had anything to do with the programming. I suspect it's just the way the program was written. (And, FWIW, I routinely tip 20% by choice, not because of how anything is programmed.)