Probably because when they worked it up for the acoustic shows in 1980, Brent echoed Jerry's line on the piano, and it made more sense for Bob to play those blocky chords behind it. Brent would usually double the line and then sometimes harmonize it later for emphasis. I saw it acoustic a few times at Radio City in 1980 but my favorite that I saw live was 1981 at MSG, where he played the line on the Rhodes and it just rang through the building like bells. Jerry really ripped it up that night. Feedback and all from the Dual Sounds, even power chords at the end. Very cool.
http://archive.org/details/gd1981-03-09 ... eok.flac16