One of the best conversations in the book, IMO, is the discussion between Elizabeth, Darcy and Bingley in Chapter 10. Not only does it have some of the best dialogue, it shows so clearly the relationship between the two friends and the developing tension between Darcy and Elizabeth. Darcy seems to be chiding Bingley for being so easily influenced by his friends and Elizabeth stands up for him, saying this is a sign of his good temper.
Why would AD leave such a revealing conversation out? It's funny, would look well, and we can't doubt the actors would have made a good job of it. What was he thinking?