Well I'm certainly not in the mood to argue on a forum about it, and since no one seems to have a definitive answer direct from Disney or Amy Adams, it'll have to remain a mystery. I myself would go with a published source before I believe anything from word of mouth.
Since there isn't much Giselle or Enchanted merchandise, perhaps Amy Adams didn't want to be typecast as that once character for the rest of her life and career so she didn't agree to signing away her likeness. Johnny Depp on the other hand, aren't they paying him something like $55 million for the 4th Pirates? I'd sign over my image for merchandise for the rest of my life for that kind of money!