I was waiting for the elevator at the end of the day, and this young man was standing a few feet away from me, talking on his cell phone. When the elevator arrived, he continued the conversation in the elevator, finishing with the comment, "I plan to go to bed early tonight."
Then it hit me--most Americans don't care about potentially being eavesdropped on illegally by the NSA, because they have gotten used to ubiquitous cell phone conversations which occur anywhere and everywhere. They get on their shiny cell phones in airport waiting areas, restaurants, subway cars, and yes tiny elevators, with no concern that their half of the conversation will be overheard by casual strangers.
They have no expectation of privacy in these conversations, so apparently they don't care if the NSA listens in too.
Anyway, that's my current hypothesis. Comments?