The difference is apples and oranges.
Cotto said he didn't want to fight at 145 unless the title wasn't on the line. He eventually caved because Pacquiao was the shot caller and that's just how it is in boxing.
Andre Ward wasn't saying Chad Dawson's name. Chad called Andre out and readily offered to fight him in Oakland at 168.
I don't have an opinion on either guy being weight drained because they signed the contracts knowing it would be a challenge to make the weight. If they misjudged that's their fault and no way should it make their loss less legitimate, and thus it shouldn't make their opponent's win any less credible.