Greetings! Many times we have clients that have trouble understanding the role of web standards and why they are important. So I created this high level explanation that I hope will suffice. It is, by its very nature, simplified and incomplete, so don’t stone me to death. Here goes…
The World Wide Web Consortium (www.w3.org) is the standards body for the internet. They define the standard “language” or markup that web pages are written in. All of our documents are written in the strict flavor of XHTML (eXtensible Hypertext Markup Language) 1.0 which is very intolerant of errors. Conforming to these standards has several practical benefits. First, the site is easier to update since all of the content is easy to read and logically organized. This reduces cost for updates to the site. The W3 provides a validator to check pages against the XHTML standard and report any errors that it finds.
Secondly, strict XHTML mandates that the graphical presentation of the page (how it looks) be separated from the actual content of the page. So there is a separate file we create called a “stylesheet” that determines how the page will look. All of the graphics, colors, and layout are determined by this stylesheet. This is a benefit because it makes for smaller, faster loading pages which can rank higher in search engines than bloated pages that are slow to load. It also makes it easier to update how the site looks. For example, as autumn approaches you could change the entire look of the site by changing the colors in the stylesheet to fall colors. This is much more efficient than redesigning a site in the old days when each individual page had to be changed at great expense.
Lastly, search engines look for unique, relevant content that is organized well. By keeping all of the content in a separate file, the content can be organized so that the most important information is close to the top of the document while repetitive elements such as the navigation links are closer to the footer.
Be sure to read this post about HTML validation for SEO
There is a great FAQ on web standards and their importance at: http://www.webstandards.org/learn/faq/