The ADA is the Americans with Disabilities Act, passed almost 30 years ago in 1990. This act was originally put in motion pertaining solely to physical location. It requires establishments to provide people with disabilities easy access to various levels throughout the business. This act was set to achieve an equal experience to all people, handicapped or not.
While legal considerations might be your biggest worry, making your site more accessible is simply good customer service. More than 39 million Americans are blind and another 246 million have "low vision," Another one million are deaf in the U.S. Add to that people with mobility issues that prevent them from using their hands and that's a huge portion of the country's buying power.
I should mention one caveat to all of this. Businesses that are required to comply but don't have the ability to bring their websites into compliance can provide an accessible alternative to provide the same information, goods, and services that they provide online, like a staffed phone line. The trick, however, is that this option has to provide at least equal access, including in terms of hours of operation. And, as we know, the internet is around 24/7, so good luck with that.
Title III of the Americans with Disabilities Act (ADA) requires that businesses and nonprofit services providers make accessibility accommodations to enable the disabled public to access the same services as clients who are not disabled. This includes electronic media and web sites. While the ADA applies to businesses with 15 or more employees, even smaller businesses can benefit from ensuring that their websites are ADA compliant. Doing so opens your company up to more potential clients and limits liability. Web developers should include ADA compliant features in the original site and application plans.