Websites always know your IP address. Some forums show you when you post. But mostly they don't let on.
Unless you're using a VPN of course :-)
Right :) Or Tor.
Yes, but I think the point is that this page's content changes based on your IP address. By commenting here about what you read there, you may accidentally give subtle hints about your location to all HN readers, not just this site or HN's servers.