I’ve been able to fix the problem by changing the default-calendar-grid.php file to change the contents of the buttons that they noted above. I ended up replacing the chevron icons in the file with stylized “<” and “>” characters, respectively. This allows a screen reader to see that there is actually content within the button, and furthermore within the table header, and as a result fixes the errors it has with the calendar.
Why was Amazon sued to begin with? Believe it or not, it was the Kindle converter for documents. Amazon has developed its own converter (MobiPocket) to digitize all the documents, books, and magazines that are shown on Kindle. But the problem is that Amazon’s converter was making it difficult for people with disabilities to access any items other than super basic documents.
If the user selects this button, the page is read aloud while text is highlighted. This is powered by ReadSpeaker, which I think is a really cool product. It provides improved accessibility to a vast audience of people who might not otherwise have their own assistive technology, such as people who are not native to the language of the page, or people with dyslexia or other reading challenges.

Use the Outline button on the WAVE toolbar to see if the web page has a halfway decent, logical heading structure. I was pleased to see that each of the 130 sites used HTML headings, but several sites had heading creep. Screen reader users benefit tremendously from good heading structure, but if a web page has too many headings, this offsets the benefits, and some of these sites have several dozen headings. If everything is a heading, nothing is a heading.

Penn in particular nearly made the cut because I really like their keyboard accessibility. It amazes me how few sites provide visible indication of keyboard focus, when it's incredibly simple to achieve (just add a style for a:focus in your style sheet). Penn did this, and consequently it's very easy for sighted keyboard users to keep track of their position as they tab through the page. They also included a keyboard-accessible dropdown menu. However, there are some dynamic features on the Penn home page that really need ARIA markup for full accessibility. They also have a few contrast problems, most notably their slideshow navigation, which is red-on-red:

When choosing an aid or service, title II entities are required to give primary consideration to the choice of aid or service requested by the person who has a communication disability. The state or local government must honor the person’s choice, unless it can demonstrate that another equally effective means of communication is available, or that the use of the means chosen would result in a fundamental alteration or in an undue burden (see limitations below). If the choice expressed by the person with a disability would result in an undue burden or a fundamental alteration, the public entity still has an obligation to provide an alternative aid or service that provides effective communication if one is available.

The large number of people who have disabilities, coupled with the challenges that they face, is one of the reasons that the Americans with Disabilities Act (ADA) was passed in 1990.² As its name suggests, the ADA is designed to protect individuals with disabilities in the United States. The ADA essentially makes it illegal for any government entity or business to provide goods and services to the general public without ensuring that the entities are accessible by people with disabilities. In today’s digitally driven world, many businesses fail to follow web accessibility best practices. In fact, this is why the Supplemental Advanced Notice of Proposed Rulemaking (SANPRM) was created by the U.S. Department of Justice (DOJ). To ensure that they are implementing digital accessibility best practices, organizations are encouraged to use the WCAG 2.1 technical requirements.³
The ADA requires that title II entities (State and local governments) and title III entities (businesses and nonprofit organizations that serve the public) communicate effectively with people who have communication disabilities. The goal is to ensure that communication with people with these disabilities is equally effective as communication with people without disabilities.