@Burnt Offerings
The ending is different in the book. The book is also way more graphic. There is no way it ever would have made it past the censors if they adapted it faithfully.
I like the ending they went with in the movie. The fact that it's ambiguous adds to it. Is Bateman killing these people? Does it really matter? He's a fucking monster either way. They all are. It's a disgusting world he lives in. Both interpretations work. It works if it's all his fantasy/psychosis and it works literally. Most cinematic attempts to pull this off feel really artificial. Bateman's descent into madness (complete with the killing and subsequent reappearance of Paul Allen) ties into both interpretations perfectly. Maybe people who occupy the upper corporate world in Psycho are so invisible and replaceable - and everyone is so wrapped up in their own shit - that people insist they are still alive when they're dead. Then again, maybe Paul Allen really is alive. It doesn't matter if he's alive, which is the point either way.
The book frequently features long (multiple page long) rants about Huey Lewis and other 80s pop stars.