The Americans with Disabilities Act (ADA), which became law in 1990, is a civil rights law that prohibits discrimination against people with disabilities. The ADA generally requires employers, state and local governments, and public places to offer reasonable services or tools to insure that people are not discriminated against on the basis of disability.
The ADA was written before the Internet was a significant force in society. Many believe that if the law were written today, the web would be included in the class of activities which should be available to people with disabilities. But it was written in 1990, so the issue of the applicability of the ADA to the web is whether or not the web can be considered a "place of public accommodation." Th Department of Justice has written that it considers the web just such a place.
On the legal front, the National Federation of the Blind sued AOL in part based on the interpretation of the web as a place of public accommodation. AOL settled out of court, agreeing to make its web browsing technology accessible. The New York State Attorney General brought an action against Priceline.com (no bricks and mortar presence) and Ramada Inns (focus on physical accommodations) saying that their web sites should be accessible. The companies agreed to make their sites accessible. To date, there has not been a court ruling supporting or denying the concept that the web, like a store or sidewalk or bus, is a place where discrimination against people with disabilities would not be permitted.
However, as you will see, making your web site accessible is a fairly simple process. And doing so increases your market. The number of people who have disabilities worldwide is significant. In America alone, it is estimated that 54 million people have a disability. You may be missing that market segment by not paying attention to accessibility. With advances in medicine and science, and with an aging population, more and more people who have disabilities, even minor disabilities, are using the computer and going to the web. If your web presence is not accessible, those millions will go elsewhere.
Making your web site accessible has other effects besides providing a positive experience for people with disabilities. Here are some other benefits:
Just as sidewalk curb cuts -- originally intended for people using wheelchairs -- also benefit parents wheeling strollers and individuals on roller blades, accessible web design benefits more than just people with disabilities. Accessibility and usability are intertwined and are equally important.