Joe... that is exactly the sort of admonition/disclaimer/warning/introduction this book needs, and I'm glad that it was included. The real problem is that it is mostly lost on those who need it the most.
People often post ...or ask about.... odd little songs from their childhood here. Yon Yonson, or Dunderbeck's Machine or recently, the one that refers to "Macedonians in full battle array"
Some one will give lyrics, and others will retype the whole thing to change one or two words! Even Dunderbeck's Machine gets argument that it should be "Johnny Rebeck". "That's the way my grandfather sang it!"
The same basic problem is seen when someone asks for the words...or chords... or tune... or all three... to some song 'covered' by someone famous, whether it is anywhere near traditional or not. They heard it that way first, and by golly, they don't WANT any corrections or suggestions!
The point is that far too many simply do-not-want to be exposed to 'new' versions... or even the author's original, if known. It is very like the resistance to new translations of the Bible by those brought up on the King James version. RUS #1 became a bible for a lot of people, and those who commit to a bible often have the notion that everyone else 'should' realize that the *truth* is somehow embedded in it.
This is not a serious problem when like minded people gather and turn to page 47 in unison... but when they appear at an open forum attended by more ...ummmm... eclectic.... folk and read (awkwardly) with the Book in their face, it makes the whole thing awkward.
   
It has been said that any book that gets people to sing & share is a good thing, and may be a first step to a wider view of traditional music.... the important term being 'may'.


(*grin* Joe... you even help make my point in your use of a tune for "The Key of R".... but perhaps the very concept embodied in the song excuses deviation. I don't see it listed in the Book.... maybe just as well.)