Green Knight says:
Instead of a slightly distant, continuous narrative, she (Austen) condenses a bit, gives us the conversation in all its detailed glory, and pulls out again with narrative when we have seen enough and any further real-time observations would be repetitive.
Good point-- a Austen-ite friend of mine (and writer) Kate Moore observes that Austen presents a conversation when it shows people in conflict, and when they agree, she just summarizes. I think that's a good way to keep dialogue important to the plot, and important to the movement of the scene. I've remembered that whenever I encounter (or write) dialogue of the "Hi, how are you?" variety. Move on; nothing happening here!