http://www.davidhewson.com/blog/2011/7/ ... logue.html
Here's one example:
Dialogue in a book needs more substance than lines in a movie or TV play. The context needs to be created quite consciously, through the passages preceding and following the speech. Actors can fill holes through the way they act, speak, respond to other players in the scene. An author has to manage the same trick the only way he can: with words. As few as possible, but they have to be there.
He's an excellent writer, so his blog is well worth following.