David Ortiz is 0 for 7 against Brett Anderson and J.D. Drew 0 for 3 with three strikeouts. So they're sitting today.
A bigger reason is that Ortiz is .201/.253/.312 against lefties this season and Drew is .185/.282/.289.
As the Red Sox look at their roster for 2011, is Ortiz a platoon player? Part of the attraction of keeping Victor Martinez around would be to DH him against lefties and catch Jarrod Saltalamacchia (or, in theory, Jason Varitek).
Maybe the same thing holds true for Drew, who will be 35 in November. If Darnell McDonald is the fourth OF, you could use him against lefties.