Uber came out of the gate with war chests from investors. Real startups that have to make actual money usually don't have investors that'll throw tens of millions into legal fees.
If your investors have indicated that they will bankroll the massive legal and regulatory issues that your company will provoke, and you believe them, then you can ignore that rule. If you're a normal person trying to start a business on your own, you shouldn't.
They didn't, though. They closed their Series A in Feb 2011. They got their first cease & desist in October 2010 [2], 4 days after closing angel financing. [3]
IMHO, the key success factor for Uber is their ability to spin every setback into an advantage. So, the fact that they were sued for operating like a taxi cab company means that the taxi cab industry views them as a threat. They could then take this to investors and say "We're about to disrupt a $16B market. The market opportunity is there, and the lawsuit against us is proof of that. The product is there. People are choosing our product over the competition. We need your help to roll back protectionist legislation that is hurting consumers. Are you in?"
And then many investors won't be, but they just keep trying new ones until they find folks who buy in.
There's nothing really technically special about Uber so I doubt that investors were lured by the strength of the proposal or anything like that. The founder of StumbleUpon was a co-founder, so it was most likely through his connections + track record, but I don't actually know the details (someone else here might). I would guess that it's just an accident of luck that Uber became Uber -- right time, right place, and right connections. That's what it takes to get a business off the ground, especially a business that raised $1.5 million in funding before it was released (per Wikipedia's timeline).
