@Rick, I didn't specifically look at doctype, but Steve Faulkner did in his original article (see the link at the top of this post). He found that 101 of the 130 pages containing role="main" (78%) used the HTML5 doctype, which of course leaves 22% that didn't. I do recommend using ARIA even if using an earlier doctype. Validation is important, but if validation and accessibility conflict, I think most would agree accessibility should trump validation. Assistive technologies that support ARIA landmarks do so regardless of doctype, and otherwise the presence of these role attributes has no ill effects in any user agent.
These impressive statistics show how invaluable a well-designed, modern website truly is. The new website draws in more visitors, encourages them to stay for longer periods of time, view more information, and inspires repeat visits. This steady traffic will help VisionCorps reach more people, and their ADA compliant design will help more people take advantage of their services.
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.
The landscape of disabled access litigation related to online services has significantly changed and expanded over the past decade. Initially, the internet was an area of little concern as courts uniformly held that the ADA applied to "brick and mortar" facilities, not to cyberspace. This has changed and online accessibility is presently, and will continue to be, an area of significant investigation and litigation.
Until the ADA is updated to address the special case of website accessibility, or the Department of Justice releases its website accessibility regulations, complying with WCAG 2.0 Level AA is the best way to ensure that people with disabilities have equal access to your website. The overview below is a great starting point about meeting the WCAG 2.0 Level AA recommendations.
...the full and equal enjoyment of the goods, services, facilities, or accommodations of any place of "public accommodation" by any person who owns, leases, or operates a place of public accommodation. Public accommodations include most places of lodging (such as inns and hotels), recreation, transportation, education, and dining, along with stores, care providers, and places of public displays. 

We not only referenced the ADA’s requirements while building the website, but also sat down one-on-one with users who are blind to see how they navigated the site. These individual sessions were invaluable and provided more insights than just the law’s basic requirements. Instead of making assumptions about how these users would interact with the site, we took the time to observe their real interactions and used that data to formulate new features.
A person’s method(s) of communication are also key. For example, sign language interpreters are effective only for people who use sign language. Other methods of communication, such as those described above, are needed for people who may have lost their hearing later in life and do not use sign language. Similarly, Braille is effective only for people who read Braille. Other methods are needed for people with vision disabilities who do not read Braille, such as providing accessible electronic text documents, forms, etc., that can be accessed by the person’s screen reader program.
...the full and equal enjoyment of the goods, services, facilities, or accommodations of any place of "public accommodation" by any person who owns, leases, or operates a place of public accommodation. Public accommodations include most places of lodging (such as inns and hotels), recreation, transportation, education, and dining, along with stores, care providers, and places of public displays. 
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