I think it's worth noting that Judah's face was bloodied, his eyes were swollen, and he had gone into a defensive shell, halfway through his fight with Mayweather. Then, when it looked more and more as if it was heading for a TKO, he delivered a low blow that caused a riot in the ring. This gave him precious minutes in which to recover - by the time the fight started again, he was back in shape.
Oh, and REGARDLESS of that, even if Mayweather wouldn't have been able to knock out Judah over 12 rounds without the riot, who really cares? Judah looked on top form that night - he boxed beautifully for around 4/5 rounds, and even nabbed the 12th round. He would have traded and delivered with any welterweight on the world on that day - he's got some of the fastest hands in the division, and his skills aren't half bad, either. His only problem is his lack of consistency.
Mayweather's not a powerful puncher, at any rate - and you don't have to be one to be the best, because boxing is about skill, technique, smarts, heart. Willie Pep is regarded by many as one of the finest boxers of ALL TIME, and he didn't have much of a punch on him.
On the matter of Hatton/Mayweather - Hatton has a decent chance. I don't like Hatton, or his wrestling style, but he can still cause Mayweather a lot of problems because of it. Mayweather loves to outbox people from middle range, taking his time, countering, slipping, etc. If Hatton is smothering him like usual, smashing him everywhere, he's going to be heavily pressured. I think he would still beat Hatton, but it'll be a close thing.
Harrison sucks. End of story.