PTT電影版剛好也有人問一樣的問題:
看了一下 IMDb 的討論區，有一些討論。
http://www.imdb.com/name/nm0634300/board/nest/108412249
我相信下面這個應該是正確的原因：
That'll be to do with writer's guild politics more than anything else. It
happens all the time. The basic structure of the movie was laid down by the
original two writers. Jonathan Nolan rewrote it (as, incidentally, did Paul
Haggis and Shawn Ryan) but the structure of the movie remains basically the
same as the original writers' draft, so they get full screenplay credit. The
Writer's Guild of America favours plot and structure over dialogue and
motivation, which is what Jonathan will have worked on.
It was the same situation on The Incredible Hulk - Zak Penn got fu...