That 90k to 30k figure for instance? http://betabeat.com/2014/05/new-york-city-taxi-medallion-man...
They don't pay the $.50 per trip tax or buying the taxi medallions which lease ~$2,500/month. http://www.businessweek.com/articles/2014-02-28/if-uber-is-k...
Mysteriously, if Uber had to spend $35k+ [or eat a one time capital expenditure of 6-7 figures per driver] more a driver, I suspect people would be thinking the $18 billion valuation was ludicrous. And realistically, since they act as a taxi service, that is what they would be paying in markets like SF, NY, etc.
They clearly would have a competitive advantage in the range of $25k/driver + taxi company like margins, but does that really justify an 18 billion dollar valuation even if you tack on a courier service?
It's also somewhat rosy to think that Uber will eat the entire market. I'm not sure an 18B valuation makes sense. Maybe a few billion, but not 18.
(I say this as someone who drives for Uber - and Lyft)
I think its worth around 10 billion [which is where the original article said VC's started dropping out of the auction en masse].
Regulations governing licensing, employee welfare, public liability, and other such, which Uber currently works around (but might not be able to indefinitely, people are looking very carefully at the situation).
Even ignoring this difference, UPS might not consider the profit margin worth the risk and the cost of the up-front infrastructure changes.