Because Calzaghe was the most blatant example of it, especially at the end of his career when his hands were so brittle, he had great stamina so could throw a **** load of punches, not hating just stating facts.
Calzaghe v. Hopkins is a good example. Hopkins was more skilled and was landing the better punches, but Calzaghe used volume punching to out score him.
I don't believe he relied on it too much though, his speed and his boxing ability were major factors in a lot of his bouts. The example below I agree with though, Calzaghe's output won him the Hopkins bout. Even though Calzaghe had a high punch output, I don't believe he relied on it.
Ray Olivera Antonio Margarito (holds the record for the most thrown punches in a 12 round bout with 1675) Juan Diaz until he met JJM Emanuel Augstus Joe Calzaghe
Paul Williams is a good shout. Others mentioned like Calzaghe didn't necessarily rely on the output, he also had stamina, chin, power (early on) and reflexes.