Secret Benefits of Accessibility Part 2: Better Search Ranking
http://www.sitepoint.com/article/accessible-search-friendly-site/

Moss, Trenton
SitePoint
2004

Abstract:

One of the main benefits of Web accessibility is that a Website that's more accessible to people is also usually more accessible to search engines. The more accessible your site is to search engines, the more confidently they can guess what the site's about, giving your site a better chance at the top spot in the search engine rankings.