I wouldn't call that a failure. They had a huge number of downloads in just a few days. That's popularity. Then they learned some valuable lessons with the experiment that could be put in practice in the future. Finally, remember that the entire (or most of) revenue goes to the band, not a record label.
My theory is that people download ilegally for the *convenience*, not out of stinginess. The next experiment, IMO, would be to sell an album at full price, but via download in a very easy and convenient way, and gauge the reaction.
So the buzz is the Radiohead "Experiment" failed.
The logic goes like this. Radiohead put their music out on a pay what you feel it's worth basis and said that they would also put it out in a regular CD later. Now it's later they are putting out the CD and they pulled the plug on the digital pay what you think part.
Thus it's a failure.
Why doesn't anyone think that maybe it's in the terms of the CD contract? That would make it no failure, Just business.