Much has been made about how John Lannan is the highest-paid player to be optioned to the minor leagues before the season. His $5 million contract heads to Syracuse, while minimum-wager Ross Detwiler stays with the Nationals big club.
The contracts of both players are sunk costs, so they lose the same amount of money regardless of how the roster is arranged. If the big earner isn't among the best players, there's no reason to bring him up.
The Giants, meanwhile, have been going back and forth with their own horrible contract in Barry Zito, who is in the midst of his $126 million deal. They left him off the 2010 playoff roster and sent him to extended spring training this year, but he's coming back to the Majors in a few days.
General managers face some adverse incentives that often lead them to hold onto big money guys or first-round draft picks too long. Letting go of these guys is akin to admitting that they made a mistake.