"Could it be that after 61 years the 1954 definition is outdated?"
It's very much in need of revising based on what we know now - it may no longer serve its purpose any more, but if we are going to continue to attempt to draw peoples' attention to the music and discuss it among ourselves, we need something we can all agree (more or less) on.
The problem lies with some of the arguments put up here by some people who argue that you don't need to define what you sing - if you confine your singing to your rubber duck in the bath, of course you don't, but if you attempt to draw people in in order to pass on the music you consider important, you most certainly do - same goes if you write about it or broadcast it publicly - "what it says on the tin".
Jim Carroll