Also - the matchups with Nava/Gomes can be more specific than strictly lefty-righty. If we are dealing with guys with excellent changeups like Scherzer - the lefty/righty thing might not be so obvious. After all, a righty-righty matchup can neutralize the righty changeup, at least a little bit. And the vs pitcher splits involve so few at-bats, that really a "scouting" based decision on who to put up there is totally reasonable.
The Red Sox interestingly have three switch hitters getting prominent run. Victorino, Nava, Saltalamacchia. None of them should be switch hitting, period. And Victorino next season - even if his hammy is ok, really shouldn't go back to switch hitting at all.