I hear you. Some people are chattier than others. Some posts are more obviously engaging than others. I except a response (in general) to meta comments, because meta is usually looking to start a conversation. I don't really expect a response to fic comments. But you're right, if they're not the sort to respond to everything, I'm cool with their not responding. I have to admit to feeling a bit slighted when someone skips over my comments in a post where they're responding to everything else. It's a purely emotional response I try to control, though. ;)