One time I was looking up the pitch counts of the infamous Spahn vs Marichal 7/2/63 game, and I came across an interview with Juan Marichal, and this quote from it has always stuck with me: "Pitch counts? You're not going to have a strong arm if you don't throw. That's why I think I threw so many complete games, because I used my arm. I loved to throw. The only way you can get a strong arm is by throwing. Today, 70, 80 pitches and you're out." I think there is a lot of truth to that, but I also tend to agree with what 'stache said with regards to pushing the envelope and higher arm stress. I think the eye test can get you to the crux of what is at play. Look at some video of any 5 MLB pitchers from say the 50s or 60s. Compare the fluidity of delivery and evident arm stress to video of 5 current MLB pitchers, especially some of the younger "flamethrowers." The difference is certainly notable.