Accessibility is an important idea behind many web standards, especially HTML.
Not only does this mean allowing the web to be used by people with disabilities, but also allowing web pages to be understood by people using browsers other than the usual ones - including voice browsers that read web pages aloud to people with sight impairments, Braille browsers that translate text into Braille, hand-held browsers with very little monitor space, teletext displays, and other unusual output devices.
As the variety of web access methods increases, adjusting or duplicating websites to satisfy all needs will become increasingly difficult (indeed, some say it’s impossible even today). Following standards is a major step towards solving this problem. Making your sites standards-compliant will help ensure not only that traditional browsers, old and new, will all be able to present sites properly, but also that they will work with unusual browsers and media.
Some consequences of ignoring standards are obvious: the most basic consequence is that you will restrict access to your site. How much business sense does it make to limit your audience to only a fraction of those who wish be a part of it? For a business site, denying access to even small portions of a target audience can make a big difference to your profit margin. For an educational site, it makes sense to allow access not only to affluent, able-bodied school-children with graphical browsers, but also to children in regions with poorly-developed infrastructure who are best served by text-only browsing, or disabled students using specialized browsers.
The same principle applies to all types of websites — while straying from the standards and taking advantage of browser-specific features may be tempting, the increased accessibility which comes from standards-compliance will lead to far greater rewards in the long run.
*Content quoted from Webstandards.org
