It's one of those situations where Wlad is the stronger, faster, overall better boxer but Vitali is smarter and tougher. Remember Vitali is pretty much undefeated in his mind, his both losses were fights he was winning then something freakish happened.
Well, against Byrd it was freakish, against Lewis he got caught with a punch and opened a cut, he was ready to go but they didn't allow him. He still feels he was cheated and doesn't really feel like a loser. In his mind and in the minds of many he is pretty much an undefeated HW because when shit got tough he just toughed it out and managed to win, while Wladimir seemed to get scared shitless when shit got tough.