Because they are so close, I'd always felt them to be of similar characters, but they actually are quite different when you look at it. Perhaps JA is pointing out that good friends come from all sorts of people, not just the archetypes found in novels.

The difference between Henry mocking small talk and Eleanor falling back on it, is that Eleanor does progress beyond it once we get to know her. Henry may be mocking the fact that even supposedly good friends (such as Catherine and Isabella) only talk about shallow topic.