The niche market of the web has continually changed over the past 15 years. Most recently, it has shifted from the Hispanic market to the 50+ age group. That shift ties in directly to designing for the visually impaired as most of us have had our vision deteriorate with age.
The Web Accessibility Initiative called WAI is only 13 years old. In terms of technology and movements it is still in an infant stage. As technology advances, so does the ability to create a more robust web that everyone can access. Screen readers are becoming much more advanced and thus they are able to interprete screens much simpler as well as more advanced languages such as Flash and Silverlight.
The main takeaway when designing to the visually impaired is to follow some basic rules when doing so: