But what if it's one of those things (like TiVo and Uber) that people think, in advance, that they don't need -- but it turns out they'll be totally hooked once they try it?
Shear mentions in the lecture that you should avoid directly asking about features or your product. "You want to learn about what's already in their heads. You want to avoid putting things there." That pretty much precludes doing things like describing your idea for TiVo/Uber to people and asking what they think. Instead, it would make more sense ask about pain points. If all of your interviews indicate that people absolutely adore the process of finding, hailing, riding in, and paying for taxis, then you'd be more justified in determining that there's a lack of interest in something like Uber.
Take your Uber example. If you'd done user interviews pre-Uber, it's uncertain whether anyone would have said "yes I want to call a black car on my phone" or not. But I can pretty much guarantee that people would have said "yes, sometimes I have trouble getting a taxi to come pick me up".
User interviews at this stage are about validating the problem, not the solution.
Get out there and empathize with real people with real problems. You'll find that even the most boring, ho-hum, run of the mill person will be happy to lay down hard cash for your game changing idea if it fixes THEIR problem.
That being said, focus groups are a horrible way to get meaningful feedback. Customer interviews and other more in depth ethnographic techniques are going to deliver what you're looking for.