This is not at all a surprise, and I fully expect Amazon to also ultimately enter this space. (I have no insider knowledge of either company.) It's amazing to me how many people think that Uber is somehow building a deep moat when these other companies (Google, Amazon, etc.) have a much deeper connection with their customers -- to say nothing of the data that have collected. Given perfect rider competition and (especially) perfect driver competition, how does the advantage not lie with the established company and brand? Given Uber's nose-bleed valuation, I suspect that they may become the Webvan-esque poster child of this bubble: visionary, but ultimately a ludicrous valuation and absurd misallocation of capital that was obvious to all only in retrospect.
Forget Google, Lyft and Sidecar are basically already the same thing as Uber. Plus local cab companies are developing their own apps. The barrier to entry in ride-dispatching is absurdly low. I wish somebody (city government? craigslist?) would just make a free clearing-house for it.
Amazon already is building an on-demand grocery service, and Jeff Bezos has long made it clear that he wants all the inventory at Amazon Warehouses to be delivered within hours to the customer. It wouldn't be stretch to think that Amazon would enter the on-demand logistics market (not just Taxi) at some point in time, cause it has got most pieces of the puzzle sorted. Same goes for Google, as it tries to take on e-commerce market with its own offerings.