As more and more content and social knowledge creation takes place on the web, conscientious people are designing their sites to be digitally inclusive. Accessibility means that the site is readable by screen readers such as Jaws. While it is possible to customize an existing WP template to make it accessible, its much easier to choose a theme that was built with accessibility in mind from the start. You can find a list of accessible WP themes here. WordPress has issued a draft of an accessibility manual, which you can consult if you’d like to learn more.