P4P isn't really black and white. There are a lot of factors built in each time the current P4P champ fights. I, personally, would say that if Hatton beat Manny (even convincingly) it wouldn't be enough to make Hatton the P4P champ - mainly based on what else Hatton has achieved recently. Hatton would need to beat Manny convincingly and then win a rematch with PBF. Then, maybe then, he could be considered the P4P champ.
But as others said, it's all just made up. Generally a tag given to the boxer out there currently considered the most talented and on form etc...