If you are ordering a web site from a design company, or from your IT department, what requirements do you give? You want the background a certain color. Your logo has to be of certain dimensions. Your site really needs to be listed in the first ten responses for a certain set of keywords in Google. What else? What about web standards?
The article Buy standards compliant Web sites by the W3C’s Quality Assurance Interest Group does a very good job of explaining why you should make conformance with various web standards a requirement of your project. Whether it’s the (X)HTML, the CSS, the HTTP your pages are served with, or even the graphics on your site, compliance with current web standards can make a great deal of difference to the success of your web site.