Working to make webpages, course materials, software, accessible to persons with disabilities is part of a larger movement known as "universal design". Universal design is about planning ahead rather than retrofitting. Its goal is to design products in a way that they are accessible to a great variety of users with differing needs.
A universal design perspective causes a web developer, for example, to think about the readers who are using older equipment, turn images off, need to use tabs rather than the mouse, access the web through speech software etc. This is not to say that web pages should be designed at the "lowest common denominator" level, and avoid using dynamic and multimedia features, but it does mean that webpages should "degrade gracefully", so that readers who cannot access or use some of the features, still experience a pleasant and coherent webpage, and have access to the information.
Some sources of information about Universal Design: