Tracking, people are far less likely to commit crimes if they need to be identified beforehand.

Background checking, while far from foolproof it's both a deterrent and a preventative measure.

Higher barriers to entry, if it takes significant amounts of effort and money to be able to drive a cab then people are both less likely to risk it and going to try something else to have their 'fun'.

Uber drivers are already identified beforehand, have to go through background checks, and, as we've learned in the article, are suspended if they are even accused of a crime. They are also tracked by GPS and probably cam, and probably will soon be tracked via other means as well (driver's door opening, etc.)

Uber isn't a ride-sharing service. Their drivers are just as tracked and identified as normal taxi drivers are. Probably more tracked than a typical limo service is.

(I also do not believe that the ride sharing services are particularly risky.)

Aren't Uber taxi tracked far better than normal taxies (i.e. GPS)?

Well, if unlicensed drivers constitute 80% of all stranger rapes (seems high, but let's take it at face value), and fewer than 80% of all drivers are unlicensed (highly likely), it certainly does seem to do something to help prevent it. Maybe easy trace-ability and filtering out of previously convicted criminals plays a part, which isn't too big a stretch.

Or alternately: people inclined to use taxis to facilitate rape are not really driving for a living anyway, and are likely not concerned about violating a licensing law.