Here are some notes on accessibility in game design from Henry Jenkins and Eitan Glinert (one of his students). Glinert has written a thesis on designing games that are accessible to everyone, including those with disabilities. He shares two key ideas:

1. When developing a game one should think about which user groups could
   play an accessible version, and which interface changes could help
   achieve that end without changing the core game aesthetic or incurring
   huge added costs.
2. Even if it is not clear how to make a game accessible, there are
   certain design principles which can be followed that tend to increase
   usability across the board. This increase in usability may in turn lead
   to accessibility.

Also, a long interview with Shigeru Miyamoto at Wired. He calls Wii Fit a "communication tool for families" and has something to say about accessibility too: "The challenge of that is that videogames then became something that
appeared to be difficult and complicated to people who don't play
videogames. So what we've been trying to do over the last few years is
find ways to take advantage of technology to essentially create an
interface that has a broader appeal and that's more approachable to the
average consumer." There's some great inspiration here and another angle on accessibility.