Well, yes (build for people) and no (stuff should be technically correct, as well).
For instance, the WGAC 2.0 guidelines require that HTML be valid, and if a client wants WGAC 2.0 compliance (even A level, not AA), the site's gotta validate [1].
unless you are doing it for bureaucracy's sake (public sector, etc.), do what works, not what some ink on paper from half a decade ago says, otherwise it's CYAE[1].
