I was going thru Bill James Online site this morning and realized that Chapman lead all NL pitchers with Win Shares at 21 and finished 2nd in the major league (Verlander finished first).
I have a limited working knowledge of Win Shares but i do believe they are a better indicator of value than WAR measurements. I'm gonna take a stab as to why Chapman's win share value is so high.
1. James believes that some situations are leveraged more than others.
2. The ballpark in which the player plays in gets taken into account better than the WAR system: something along the lines of Chapman saving a run in a high run environment is worth more than in a low run environment. Since GABP is a hitters park Chapman's production is worth more than say Kimball -who pitches in a park where runs are scarce. I know the WAR system takes that into account, but i really do believe they WS system does a better job of evaluating value.
Maybe the Reds are maximizing Chapman's value by keeping him in the bullpen.