The ADA itself holds different organizations to more/less stringent standards based on a host of factors, government funding being a major one. Government agencies themselves are usually held to the most severe standards. That said, while ADA has adopted WCAG as the defacto standard, from what I’ve seen it appears they’re going with AA compliance as the most reliable one. That said, we’ve done work with some organizations who’ve chosen to comply with AAA in an effort to be as buttoned up as possible from an accessibility and experiential perspective. We’ve also worked with some who have tighter budgers and aim for level A compliance and have a more “react and repair” mindset when they discover anything in their site that is giving someone hardship from an accessibilirt standpoint.
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.
Spector v. Norwegian Cruise Line Ltd. was a case that was decided by the United States Supreme Court in 2005. The defendant argued that as a vessel flying the flag of a foreign nation it was exempt from the requirements of the ADA. This argument was accepted by a federal court in Florida and, subsequently, the Fifth Circuit Court of Appeals. However, the U.S. Supreme Court reversed the ruling of the lower courts on the basis that Norwegian Cruise Lines was a business headquartered in the United States whose clients were predominantly Americans and, more importantly, operated out of port facilities throughout the United States.