Federal law isn't the only consideration for businesses. Additionally, each state interprets the law differently. Consider the case against Netflix in 2012. Lawsuits were brought in federal court in Massachusetts and California. Netflix was accused of violating the ADA by not offering "closed captioning" options for its Internet streamed movies. Illustrating the complexity of this issue, the courts reached completely opposite decisions. Massachusetts held that Netflix must comply with the ADA, while the California court found that Netflix did not fall under the ADA's definition of "public accommodation."
The Americans with Disabilities Act (ADA) was first passed in 1990. Twenty years later, the US Department of Justice released an update called the 2010 ADA Standards for Accessible Design. These standards cover the design of physical spaces and have been interpreted to include web locations as well, so it can be difficult for the would-be accessible website designer to use them.
You may have installed a ramp, increased the width of your door frames, or made other accommodations to ensure that your physical premises are accessible to all. The requirement for equal access used to only apply to physical locations and storefronts, but now the government is actively ensuring that the requirements for ADA accessibility include online properties such as websites and mobile apps.