Form Versus Function in Art
Soundgarden in the heat of the grunge movement:
It's gnarly, dirty, and full of energy.
Versus Breaking Benjamin's post-grunge pop music:
Over-produced, calculated, polished, and posturing.
EDIT: i.e., the chord structures and rhythmic structures are not too different, but the production style, the drumming style, the vocal style are all an evolution, but the underlying musical concepts are not that different. So the form, the style, is the only thing that's evolved; the technical information underneath the style hasn't evolved all that much (a little bit, sure).