good facial animation is very difficult to do with bones. i think most 3d artists prefer to use blend shapes. it's easier and more fun to work with.

why would it require fixes when the model turns its head? mixing blend shapes with bone animation works great in programs like blender.

i don't think it would take that much memory since it mostly would only affect the face vertices and you wouldn't have to store whole vertex animation sequences but only a set of blend shapes. animation sequences could be done per script or in the model format there could be a list of percent values for each sequence.