ADA compliance isn’t a set-it-and-forget-it thing. Compliance standards must be followed and will evolve just as your website does. There are guidelines all website contributors must know to stay within ADA guidelines. It is generally not burdensome but it does require some web managers to change their workflows. For example, loading images up to your ecommerce site will always need some of that alternative text (alt tags) mentioned above.
Olmstead v. L.C. was a case before the United States Supreme Court in 1999. The two plaintiffs L.C. and E.W. were institutionalized in Georgia for diagnosed mental retardation and schizophrenia. Clinical assessments by the state determined that the plaintiffs could be appropriately treated in a community setting rather than the state institution. The plaintiffs sued the state of Georgia and the institution for being inappropriately treated and housed in the institutional setting rather than being treated in one of the state's community based treatment facilities.
Web designers often design in such a way that does not allow the user to adjust font size or color. While they may be protecting their brand, they are also inhibiting some users. Many visually impaired need to use high contrast color settings or very large fonts to read a website. Don't design your website in a way that makes it impossible for them to do this.