You are correct, ADA defines an “employer” as any person who is 1) engaged in an industry affecting commerce; 2) employes 15 or more full-time employees each work day; and 3) for at least 20 or more calendar weeks in the year. In the context of physical spaces, ADA would not apply to companies with fewer than 15 employees. However, courts don’t seem to have come to a consensus on what digital compliance really should look like. Because websites can be accessed anywhere in the country, small business owners might potentially face lawsuits in unfavorable jurisdictions. If you are a small business owner, I would recommend consulting with an accessibility lawyer and ask what they recommend.
Yes, in time non-ADA compliant websites will be penalized in the search engines. It's already on their radar. But for now they are still negatively affected, just in an indirect way. Live traffic behavior (user experience) is now factored into Google's algorithm and is a ranking signal. Negative user interactions absolutely have negative affects on rankings.
If your hotel used responsive web design when creating your online marketing strategies, you’re already meeting many of the ADA compliant regulations for hotel websites. You will still need to make some changes, but you definitely have a head start. Making the changes now, before your business is the target of a lawsuit or government action, makes good business sense.
The legal issue for websites is whether website operators are operating “a place of public accommodation.” The statute lists 12 different types of public accommodations including somewhat of a catchall that includes “other sales or rental establishment.” The list, created when the law was passed in 1988, conceivably covers most commercial establishments, but does not expressly include websites.
Courts have essentially taken three positions when approached with this issue. Some courts take the position that the ADA applies to all commercial sites because the law was meant to protect disabled individuals from having a more difficult time than able-bodied individuals from doing business. That is why the website Scribd was unable to get a case summarily dismissed and ended up settling.