That would incentivize riders to rate their drivers lower.

Then don't attach tips, though maybe this would allow for more accurate reviews? I always give 5 stars, because its easy and all rides have been great.

Only one driver though, provided me with water bottles and candy. That was a superb experience. Maybe the only superb one while the rest were fine.

Really? The "upper-class" people who use Uber (people who are using their expensive smart phones to order the cab, people like ourselves) are averse to tipping well when the service is great? That's disgraceful.