You're wrong with that one dude. Actually, you don't even need a copper membership in order to make good posts, right knowledge and/or experience is quite enough. Meaning, the quality of your posts doesn't rely on the account itsself but on the user. Even if you have a Legendary account here in the forum but you are only a beginner in crypto world, that account would be pointless.
That thread is the new implemented rule by theymos. I think you mean this: https://bitcointalk.org/index.php?action=credit;promote