Apple has long been a distant 2nd when it comes to accessibility solutions. Microsoft has put more effort into a reasonable foundation, and 3rd party vendors have built on top of Microsoft's base.
Recently, though, Apple has tried a bit harder. Legal threats from several states and fears of being shut out of the education market may have provided valuable motivation. (See: section 508.)
For example, OS X 10.5 has an improved screen reader, though Apple still has a long way to go. On the other hand persons with joint and motor disorders want robust voice commands and speech-to-text recognition -- but OS X provides only the feeble and under-developed "Speech Commands" tool.
In addition to the improved OS X accessibility page (still heavy on the marketing) Apple now has a 3rd party OS X accessibility page. Unfortunately, some of the solutions are only mildly related to accessibility and a few are basically web services that work on any reasonably browser.
There's a general accessibility page for all Apple products with some links I'll explore, such as the lioncourt blog.
At the moment I'm focusing on things I can do with for my mother, but the combination of poor vision, bad joint disease and limited sensation puts things beyond what Apple can do. Now if she had a way to say "open mail" and "read messages" and then listen to the messages ...