well, that is a good question.
But honestly, I think what will eats up most of the storage capacity is the full motion video especially one runs in high definition. it will eat up more information than sound, real-time environment, texture, and other programming data combine. Even if FMV uses more efficient codecs like MPEG-4, or VC-1...
I guess that is the major reason why DOA 4 nearly runs out of space mostly because of HD Video CG FMV...