Tramadol is highly addictive. Work for a drug treatment center that handles healthcare professionals and you'll see. It's politics that got it off the scheduled list (lobbyist power). Just do a search on tramadol addiction and you'll see. Some say it's worse than getting off low dose methadone.
Darvocet is a narc (look up the scheduled narc laws about locks and counts and that will shed some light why some are highly prescribed, others aren't).
Vicodin used to be a class lower than percocet (not sure if it still is) but it was just as powerful...all politics when it comes to scheduling