[embplat]

Read about WCAG (http://www.w3.org/WAI/intro/wcag), that's what you need to follow to make web sites accessible, not markup validation, which really means "jack shit".

Visual impairment does not necessarily equal total blindness. Accounting for text size, contrast level, etc. is a lot to consider. AA conformance level (middle level, so to speak) is very hard to achieve.

[nness]

The Australian government made WCAG 2.0 a mandatory requirement of all government sites. Many claim to conform to the Double-A requirement, but very few bodies do accreditation and the standard itself is almost incomprehensible.

A List Apart did a pretty good article on the issues with WCAG 2.0 in 2006: "To Hell with WCAG 2" http://www.alistapart.com/articles/tohellwithwcag2

[embplat]

The Canadian government is in the same boat. In fact, they are offering an open source framework that is modern, responsive and complies with WCAG requirements: https://github.com/wet-boew/wet-boew

[embplat]

Here's a Wired article on this subject from today: http://www.wired.com/wiredenterprise/2013/01/wet/

[silktide]

Many web devs use the W3C validator and assume the green tick means it's completely accessible. But they can only check for so much, which makes it almost useless. There's no substitute for actual user testing