You can add location information to your Tweets, such as your city or precise location, from the web and via third-party applications. You always have the option to delete your Tweet location history. Learn more
This injects extra noise into the system. On the HN comments for this, plenty of people say they'll give a decent ride 3 stars because that's the "right" way to rate. The fact that you can usually average this out doesn't mean that noise has no effect.
An alternate rating system that has the exact properties you describe is: 60% of the time, the driver gets the rating you give, 40% of the time, it's inverted. Sure, that can work, but I don't think being able to average out the impact of noise is a particularly strong defense.
