The names were changed since it was later discovered that there were real people who worked on Wall Street with those names, and they production could run into trouble down the road. In the book their names are Timothy Price, and Paul Owen. In the novel Timothy Bryce and Paul Allen have mildly different surnames. In the film he is a much older character played by Willem Dafoe.
Some Minor Differences are, The character of Donald Kimble is a man around Bateman's age, 27, or 28. Yet due to run time, and content wise, there is much that is different from the novel. There is also many similarities or things taken directly from the novel. There are many differences from American Psycho the novel, and the film.
