Nitro varies greatly depending on how much plasticizer is used in the formula. Plasticizer will prevent the nitro from cracking, but it also makes it feel very sticky. Paul likes to use as little plasticizer as possible because he feels plasticizer deadens the tone of the guitar.
Very interesting, Shawn. Intellectually, it certainly makes sense that the more rubbery/gooey the finish, the more it would tend to deaden vibrations.
Whether that is in fact the case I will leave up to Paul's most excellent hearing acuity. There's certainly no question that my acoustic sounds great!