Fake Plastic Song

There's a new old project in the works called 7 Worlds Collide featuring an all-star list of musicians, including Ed and Phil from Radiohead and Wilco's Jeff Tweedy.  Check the vid below to catch Jeff Tweedy laying down the vocals for a cover of Radiohead's "Fake Plastic Trees."

Philosophical question of the day: Is this still a cover song if 40% of Radiohead (e.g. Ed & Phil) is featured in the performance as well?  Or is it Radiohead featuring Jeff Tweedy?  If not, then how many members of a band does it take to pass as the original?  In Radiohead's case I'll go out on a limb and say that if any one of the members is not present, it just quite isn't the same.  There's something unique about those five guys playing instruments together that doesn't happen with just any group of people.