This is another way to think about Uber's valuation - the license to operate a yellow cab in NYC is a tradeable asset whose value can be observed. The value of all licenses in aggregate, comes to about 13 billion, give or take a few. And that's just one city.

http://www.slate.com/articles/business/moneybox/2012/06/taxi...

http://blogs.reuters.com/felix-salmon/2011/10/21/why-taxi-me...

http://nypost.com/2014/02/26/taxi-medallion-auctioned-for-re...

http://www.nytimes.com/2013/11/15/nyregion/1-million-medalli...

You can make an argument in both directions. On one hand, clearly the taxi industry is large enough to justify this kind of valuation or even much more. On the other hand, Uber currently benefits greatly from this legally enforced supply restriction that chokes off their competition while not yet applying to them. Most large cities can dramatically lower the cost of and increase the availability of street-hail cabs by issuing more permits, which can cut into Uber's revenue. Cities can also decide to apply more regulation to car service businesses or even Uber-style businesses more specifically to even the playing field.