It has been years since i have had to manage web design stuff...but as i recall, section 508 specifically calls for federal-centric web properties to - by law - include accessibility features to accomodate the American Disabilities Act (the ADA). So, yeah, it better damn well have accessibility baked in, else it would be illegal. :-)

To be fair, the little documentation and blog posts here and there that i have read on the US Digital Service is that those folks reaslly are attentive to design considerations for always including accessbility...which is awesome!!