I was a big fan at the time and paid $0, I read later that most people did the same but that a good amount of people did pay money, and the album was more profitable than their previous album. I felt a little bad and later bought the physical copy when it was released. It's either the best, or second best Radiohead album. It's definitely worth listening too.
Some people, like GP, or me, might pay for something just to reward a step in the right direction.
Band I don't listen to releasing music I don't listen to in a way I prefer might be a step in the direction towards band-I-listen-to releasing music in a way I prefer.
Basic psychology. Works on pigeons and what not, as proven by B.F. Skinner.
But I am unconvinced when it comes to the content industry, I'm not sure we can repeat the success from the pigeons on them ;-)