There are now some authors who are getting music commissioned to be heard whilst reading their books: see Peter F. Hamilton's recent The Abyss Beyond
Most of the time my major characters walk into my head and announce they want their story told. Then we have a sort of audition (is their story a novel
This is one of the most valuable things a reader can tell a writer: where in the story the loss of interest/boredom/annoyance or the confusion happened.
Personally, it has nothing to do with the label "prologue", and I doubt it's that with editors, either. I've done books with, and without them.
Legacy is actually a prequel to Eon - not quite a standalone as it helps if you've read Eon first but you don't need to read Eternity before Legacy.