And so many went on to buy the CD version, and some bought the deluxe edition, with a second disc of exclusive tracks -- which were only exclusive until they were later released as B-sides.
You can look at it as either a way for the band to accept tips from their fans, or more cynically, you can look at it as double or triple-dipping. Regardless, Radiohead weren't looking to pioneer some new business model when they did the pay-what-you-want In Rainbows download. They didn't share any information about their experiment with other artists.