"Renoir’s method does away with self-consciousness and a glib spontaneity," says Raymond Durgnat, "and yet, it allows an unself-conscious spontaneity independent of the actor, and of Renoir, to develop beneath."
It is very interesting the way Renoir casts his films. As you said, he avoids typecasting, but that creates an interesting effect. By casting someone against type, you see them acting differently than they would otherwise do, the end result is a sort of interturmoil that exists in that character. I guess the best example of this is in Rules of the Game when Marcel Dalio's character reveals his music contraption.