I've built a library for iOS (https://github.com/bennyguitar/libHN) that handles scraping, commenting, submitting, voting, etc pretty well and allows me to make as few web calls as necessary to use HN. It looks like I'd have to drop functionality and completely change the networking scheme to match this API - something I'm not willing to do yet.
Correct me if I'm wrong here, but to get every comment on a post, I'd have to recursively get each item for each child. Instead, right now, I can make one network request and get all comments for a story. Granted, I have to parse the HTML (which I hate), but it's a much cleaner solution than going through every item, checking the children and then getting those items ad infinitum. Again, I just glanced over the documentation, but that seems untenable to me.