I think the difference is I view AW's structure as choosing a particular tempo, scale, and style, rather than choosing the notes ahead of time. They're just a particular set of constraints so that you produce music that has certain qualities to it.
That's actually the problem for me - see, if Cash had AW's advice when creating Hurt, would he make it a touching story about an old man looking back on his life, instead of a story about a guy loosing a girlfriend?
Of course, that's just making the metaphor even more convoluted, so let's cut that Gordian knot a bit.
By the very idea of mechanic, creativity in RPG, at least by a normal definition of creativity, is constrained - and that's alright. Because I am not looking for a creative venue as a storyteller in an RPG, but for immersing my players in the best experience possible. Of course, there IS a place of storytelling creativity in RPG, you just need to remember that the show's about the players and their characters, not about your intentions for them.
So, since creativity is already quite restricted in RPGs, why restrict it further by making claims about needing a very specific kind of such creativity for a game? Even worse, instead of allowing a GM to experience mistakes, and forge his own opinion, there's a small attempt of forcing an opinion on a GM.
And that's all, really - a normal RPG gives you all the composing and singing advice you need. Some will do it better, some will do it worse. But to try and claim that there's One True Way to play a song/compose a song, because that's what genre requires - is a big no - no. I mean, musicians even probably claim that - but most of the true splendid works happen, when a guy takes the most obvious song from a genre, and shows how much of a different spin you can put on it.
And I don't think there's anything wrong with tweaking things if you want to, but you're not going to use the same methods to produce bebop jazz and progressive rock.
True - but that's what GM Advice is for. Nobody really expects you to run CoC the same way you run DnD, but there are many ways to run CoC as well. Some prefer Purist - style tragedies, some prefer a bit more Lumley.