There’s an article on A List Apart called High Accessibility Is Effective Search Engine Optimization which, while not saying anything revolutionary, is a useful paper to wave under a boss’s nose, along with Google’s advice to web developers.
I’m certain that it’s the case that developing an accessible standards-based site helps your Google rank. Some time ago, I redesigned a web site for the small not-for-profit Waterworks Jazz club as their old site was a bright pink anigif-ridden tag soup that didn’t say “Jazz” or “Art deco” so much as “Prawn Cocktail” and “aesthetic apocalypse”. Obviously, the redesign was with standards and accessibility in mind while trying to be reasonably pleasant on the eye.
I had a phone call from the site owner last week, who told me that they’ve had several newcomers to the club lately. When they were asked how they found out about the club, they all replied “from Google”, as it’s been the number one search result for “jazz club birmingham” since it was launched.