Scraping works for operations that require login as well. You just have to start with the login process and hold onto the cookie it gives you after you post to the login form. As long as you continue to send your cookie along with each request you'll be able to access any information you want, as well as automate things like voting (not recommended). I haven't seen anything that asks for my HN password yet. Usually they just ask you to create a separate account with them and will scrape your profile looking for an authentication string to verify your HN account. What apps are you referring to?
Edit: Nevermind, you're referring to scraping only working in scenarios where you're the one doing the scraping -- not some external service. In that case, an API would be useful. I'm not sure about the usefulness of the apps though...
