I was going on an Emily Haines/Metric binge the other day, watching all their interviews on YouTube, and came across this one where Emily Haines and the lead guitarist for Metric, James Shaw, were being interviewed by BiteTV. In it, the two speak on the writing process and the evolution of songs through live performance, and the interviewer brings up the idea of "demo-itis," or the phenomenon of a listener hearing a demo of a song and attaching him or himself to it to the point that when the final studio version appears on the record, it's ultimately a disappointment because one has grown accustomed to and fond of that demo incarnation of the song. In response to this concept, Shaw comes up with a beautifully articulated answer that begins at about 5:14.
What Shaw explains seems especially permanent with Radiohead, namely on In Rainbows. Many die-hard fans ended up disappointed with the record versions of "Videotape," "Nude," and "Down Is the New Up"—just to name a few. However, with Shaw's perspective in mind, it makes more sense that the disappointment arises not from the final product being lackluster or unsatisfying, but rather from the fact that it is just that: a final product. That is, it's reached its final form and the infinite musical possibility once had been is now rather dishearteningly consummated. At the risk of getting too Radiohead-centric, I would argue that this why such tracks as "Big Boots" and "Lift" are better off living on in bootlegs, the alluring possibility of what could have been adding that air of the unknown which makes the listening experience all the more captivating.