agreed
I see the others have explained the difference
this might help
http://sportsillustrated.cnn.com/2008/writers/tom_verducci/02/05/verducci.YAE/index.html
Why can't they throw 200 innings? Simply put, they're not conditioned for it yet. It's like training for a marathon. You need to build stamina incrementally. The unofficial industry standard is that no young pitcher should throw more than 30 more innings than he did the previous season. It's a general rule of thumb, and one I've been tracking for about a decade. When teams violate the incremental safeguard, it's amazing how often they pay for it.
Pitchers generally feel the effects of abusive increases in workload the next year, not the season in which they were pushed. In other words, you might be able to finish that marathon for which you didn't properly train, but your body will have hell to pay for it. I call it the Year After Effect.
Here's the way I track it: Find major league pitchers 25-and-under who broke the 30-inning rule. In some cases a pitcher's innings the previous season may have been artificially depressed, such as by injury, so I'll use his professional high for the baseline, or, in the case of a recent draftee like Kennedy, his college workload. All innings count (minors, majors, postseason).
In 2005 and '06 I found 17 pitchers I defined as at-risk of the YAE. None made it through the next year without an injury or a higher ERA. Ten of them broke down, the most seriously hurt being Francisco Liriano, Gustavo Chacin, Adam Loewen, Scott Mathieson and Anibel Sanchez. Eleven of them had worse ERAs, by an average of about a run and a half. Remember, it's a general rule; there are exceptions, the superlative Justin Verlander being one.