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].
http://www.alistapart.com/articles/tohellwithwcag2 "To Hell with WCAG 2" (2006)
[1] cover your ass engineering