I'm not usually a nut for accessibility, but you make a good point. Using semantic HTML tags and a few other basic best practices (e.g. alt/title attributes, sufficient color contrast) goes a long way.
Depending on the juristiction your customers operate in, any accessibility issues could also expose them to legal liability for non-compliance with various laws (eg ADA in the US, the Web Accessibility Directive in the EU for public sector bodies)