I wish Hacker News didn't use it. It's a PITA logging in! I don't see it when I'm in the U.S. but when I'm overseas...
Are you sure it is HN that uses ReCAPTCHA?
If most users don't even know that ReCAPTCHA is used, that's a good sign that it is being used as little as possible, though.
Either HN has changed or they now conditionally load it. For example, I encountered it every time I used Tor on HN, though I haven't hit /login in months.