I've often wondered this myself when designing login forms, but doesn't identifying which field failed expose a security issue? A malicious user could use the feedback to determine if accounts exist or not. This seems like a concern to me.
Half of the advice in this article is terrible. Never tell the user which field they got wrong. Also, if you're going to allow signing in from any page then every single page needs to be transmitted over HTTPS in order to prevent a man-in-the-middle attack. The author really needs to think of issues outside of plain usability before writing articles like these.