They were actually talking about this the other day on ESPN (I know, I know) and they made a pretty good point about the fact that with the increase in training and such - both hitters and pitchers are better than they were 'back in the day.' Their point to this was that some pitchers from years past talked about being able to 'coast' for a few hitters, but now days there is such an emphasis on offense that even 7-8-9 hitters on many teams (the area where a pitcher may have been able to throw less than his best stuff before) are talented enough to require a pitcher to throw more of his best stuff. Which means more strain on the arm, and more breaking balls - which is harder on the arm.