The problem with considering the lift vector for reestablishing roll is that roll really has little to do with gravity or the wing's orientation to the earth. The lift of the wing, either side or the whole, has little to do with how level it is in relationship to the earth. That relationship has something to do with how well an unlevel wing carries the load when the wings are not level, but not much with how either side's lift will work to bring the wings back level.

http://en.wikipedia.org/wiki/Dihedral

Wikipedia says it pretty clearly. And mentions the common misconception about the lift.