I agree to a point, there will always be extreme examples one way or another however. Guys like Ryan who should have thrown their arms off, and then guys like Prior with "perfect" mechanics who can't stay healthy longer than a few starts in a row it seems.
I think I am somewhere in the middle. If the pitcher is cruising and doesn't show signs of fatigue, leave him out there, even if it is 120 pitches or so. Obviously if he is struggling, it's time to get him out asap.