It's just an old adage and saying. Plenty of champs have been dethroned on close decisions with close rounds. The edge that the champ has is keeping his title in a draw. With so many titles nowadays, it's more about being a "star" as opposed being a "champ".
Which is subjective to scoring and why i said every judge mays ee things differently. As long as there is no outright corruption we need to put ourf faith in a scoring system that does in fact work in a gray area.
On a round by round basis, if the challenger and champion are pretty equal in a single round, this is usually a champion's round. The challenger has to impress to win the rounds and if he wins enough rounds then he takes the title.
i hate this saying. it was brought about to excuse robberies in the past. if you win a fight, you win. it's as simple as that. the title doesn't change the way a fight is scored.