Response to Spark:
Actually, from what I've heard and read, the reason the characters names are the same as the actors is so that they didn't need to worry about someone 'breaking character' (pulling out of the emotion of the scene) by accidentally letting someone's real name slip out. This way, even in times of mental duress, etc., the directors didn't need to worry about an actor screwing up in the middle of a good improv. Since a huge percentage of the movie was improvised, and the excitement and drama came out of that improvisation, to shout cut and retake a scene is completely out of the picture. Keeping the actor and character names the same takes that one variable out of the mix.
chizpuf