I always thought the only difference between an original version and a movie tie-in version was that they changed the original cover to a still from the movie, and that's it. However, on another forum I frequent there's a guy who says movie tie-ins often change stuff in the book so it's closer to the movie. Books he says where that happened are the Eragon series, My Sister's Keeper, the Twilight series, The Golden Compass and The Help. I can't find anything about this on Google, and it just seems counterintuitive to me. They'd have to actually put effort in that, instead of just slapping on a new cover.
Can anyone debunk or prove this?

