Absolutely conditioning is part of the equation. Guys like Livan Hernandez, Zambrano, and Sabathia appear to be outliers, though. I can't agree with the last sentence, though. Pitching while fatigued is never a wise thing. As in your example, it may (and does) take Z more pitches to get to that point than Marshall, but once he is there, he should be removed. There have been several games this year when Baker has allowed Z to continue to pitch when he clearly had lost his mechanics and was laboring to get the ball over the plate. That's just foolish. The facts back this up. Hitters (except those managed by Dusty Baker, who's still living in the 60's), are seeing more pitches per plate appearance, and, on average, more hitters are receiving plate appearances per inning than in the past. While pitchers might have thrown more innings in the past, they were generally throwing fewer pitches per inning (and per outing, perhaps).