I use three fingers as well when picking, but I have to say that I am in total disagreement with those who perceive thumb and index finger as being somehow limited.

the reason for my disagreement is This

I have tried for over two years to duplicate Doc's fingerpicking on this song , and just cannot do it.

furthermore, I do not believe anybody else can either. There are a few wannabees on Youtube who attempt it but none of them come even close.

strange how something which looks so simple can be so damn difficult...