Designing websites that are 'Accessible' simply means building sites that cater for all types of web users. A website should look good across various browsers, such as Internet Explorer, Opera and Netscape.
More importantly, an 'Accessible site' should also be able to be used by people with disabilities such as those who are visually impaired.1. It is the right thing to do
2. It is legally binding in some Countries (example the USA) and will be across the web very soon.
3. According to research, 10% of all Internet users are disabled in some way. If you do not have an accessible site, you are cutting off 10% of your potential market......it is good business sense !