@Steve Jordan
This is still a slightly different situation. No one is suing to force Amazon to add features that benefit the disabled, they are trying to force them to REMOVE a feature.
It's important to understand that Amazon is not selling anyone an audio version of anything - the user is using a tool to interpret pure text. This would be akin to accusing a music store or a piano company of selling CDs because a someone bought some sheet music and decided to play it at home for themselves.
While this might not fall strictly under ADA territory, the Kindle, with it's TTS engine and ability to display large text, is the perfect tool for those with visual impairment. This is not a fight I would want to have anything to do with.
I don't know about you, but I'll be avoiding anyone on this list for the time being.
http://authorsguild.org/news/member_websites/a.html