Moneyball is about asking simple questions of baseball, and then finding the answers that no one else has thought of.
Q: How much is 6 innings of 3 run ball worth?
A: Much less than the current market rate for 4th and 5th starters.
The Yankees have had the top payroll in baseball for over a decade now, but the rest of the league didn't start to tremble until the front office started deploying those dollars for maximum efficiency. One of the best moves of Brian Cashman's tenure, I think, is the transition from the high paid setup man (Karsay, Gordon, Farnsworth) to stocking that role with arms from the minor leagues, whether starters trying to make the team (Joba, Hughes, Aceves) or young fireballers (Robertson, Logan, Kontos).
Building a pen from the farm has a number of attractive benefits. First, unlike a position player, who needs a degree of skill and familiarity before shifting positions, pitchers attack batters in similar ways regardless of the inning, so stocking a 4 or 5 man bullpen from the farm is much easier than stocking 4 or 5 starting position players. Second, reliever performance is legendarily volatile; it's a small sample size and player performance is close to unpredictable. Using players with options for the bullpen gives the manager a chance to mix and match, playing the hot hand as much as possible by sending a struggling pitcher down to the minors. Third, since young players are cheap players, that leaves more payroll for other parts of the roster. If 5 guys out of 25 make peanuts, the $200M payroll can bring in much better players at the other spots.
What I've come to love about 2011 is that the Yankees basically applied that strategy to the 5th spot in the rotation. If Bartolo Colon had been worthless, would anyone have blinked twice? If Ivan Nova got shelled, who would have been surprised? Adam Warren, Hector Noesi, DJ Mitchell, Betances, Brackman and Banuelos have all been waiting for one more injury to get their shot at the big leagues. One of them could handle the rotation, at least for a few weeks. And if you needed to swap them out throughout the season, so what?
This strategy isn't for every team. For years now, the Yankees have focused on drafting and developing arms. Most teams are not as pitching rich as the Bombers; but how many of them could have been brave enough to go into the season with CC Sabathia and a prayer, and still earn a 5 game lead in the division with 14 to play?
MLB is scared of an efficient Yankee franchise- hence all the noise about adding a playoff team. The Yankees could have thrown money at an Eric Milton or a Braden Looper. Instead, they trusted their scouting department (I think it was Tony Pena who called the scouts in to watch Colon) and their minor leagues. Let somebody else spend impact money for replacement level players. The Yankees are following a good strategy in only offering top dollar for top players.