In my opinion, the key asset Uber has is their driver network. Like you say, anyone can build a similar app pretty quickly, but who will use it if there are no rides available? They've paid so much into user acquisition precisely so it is more appealing for drivers to join the network.

In this light, the CMU investment makes a ton of sense. It's going to be extremely difficult for any other competitor to get the critical mass of drivers that makes grabbing a ride a <5min request, except in the case of driverless cars. GM (as an example) could quickly put them out of business by partnering with google and deploying thousands of self-driving cabs in a city and slapping an uber-like app on it. There's no other way to get that many drivers.

Obviously the above example is a longer-term threat, so to say that anyone can just build an app and outcompete Uber is missing where the real value in Uber lies.