Watched the Patterson Johhasson fights the other day, man both of them were on the floor more than the carpet. Neither man could take the punch of the other, I think that Johhansson hit harder but Floyd was in better condition.
That's usually because the loser is able to adjust and counter what happened in the first fight. Then in the winner of the first adjusts again to the new tactics and the 3rd is good. The loser just plain has more information to work with.
Great point escudo, the reason they have a rematch is that the fight was evenly contested and the skill of both were mostly at the similar level. And since we are talking about great trilogies, the first fight most of the time must a great one. And usually the loser of the first realise his mistake and took a different strategies in the rematch, so the rematch usually not as great as the first. The third usually is a carbon copy of the first as pride got the better of them.