Coldplay vs. Radiohead vs. NIN

DOES FREE MUSIC = MORE POPULAR?

How does "free music" effect a band's popularity?  An analysis by Hitwise (via DMW) showed that Radiohead's release was much more popular than either Coldplay's or either of the Nine Inch Nails releases, as measured by US Internet visits.  Radiohead also did a much better job of sustaining interest.

Why did Radiohead rule the net since Coldplay is a more popular band by most other measures? Was it because they were Radiohead was the first major band to go free?  Or was Coldplay's single song limited-time offering just not enough to grow and sustain fan interest?