Yeah, it's in the key of D. But goes to a G base on the first phrase which is really voicing a G chord. Then back to D. Then a descending base line under the D chord going C-B-Bb. Then back to D. Then a riff that slides up the neck to some other quick chords (F and G) and then back down to the D chord. Then on the chorus it goes D - A - G - A ...then the quick F and G slide.

Only I think Bob's got it capo'd up the neck a little. I'll have to check by listening to the original recording.