Exactly, Uber needs to scale along axes in a way most traditional web companies do not. The axes have been pointed out are heterogeneous city/state/nation regu

Exactly, Uber needs to scale along axes in a way most traditional web companies do not. The axes have been pointed out are heterogeneous city/state/nation regulations, labor law, naviagation/connectivity issues, etc. And onto each of these diverse cases, there needs to be a way to analyze results consistently and deploy business objectives from a centralized corporate strategy. As you point out: to justify its unicorn status, Uber needs to prove that it can succeed not just in competing with taxis in the major markets where it already exists, but that it's technology platform can be deployed to the edge cases, and the areas where it hasn't. So what the extra engineers are doing finding a way to acheive user reliability under the reality of accelerating changes to requirements and sharding of policies for separate operational units that will result from forced-growth into non-optimal markets.