Uber doesn't buy and own the car, which means it requires much less capital. This small change has many implications, and the tech helps solves many of the problems that come up.
I am not saying it is properly valued (over or under or whatever). Just that given the choice between an Uber (or Lyft or yourlocalapp.com) or a cab company with the same fleet, customers, and revenue, I would consider the Uber version more valuable.