Standards based design separates style and content by placing the design elements into separate style sheets. These style sheets can be applied across all pages in your site. This creates a consistent look and feel for your site.
Search engines are more sophisticated today than in years past. They focus on page content and not so much on meta-tags. By removing the style from the content, search engines have access to more of your content. This results in better search engine results for you.
Updates to pages can be done without having to worry about "breaking" the design, this saves you time and money.
Complete site redesigns can be done without changing the content on the page. Simply apply a different style sheet and instant site redesign.
Standards based design provides better accommodation for cross-browser compatibility, accessibility, and different types of media (Cell Phones, PDAs, screen readers). This allows more people to experience your website the way you intended it to be experienced.
