Making it much easier for those of us who are challenged with web-development, Gustafson compares this idea to the structure of a Peanut M&M.
Tiffany Tse also raves about this strategy in her article. With technology and browsers progressing and changing so frequently, we need to employ progressive enhancement in everything we do. Having a rich, thorough core (i.e. content), we can continue to layer on top of that while ensuring the web is accessible to all current and future browsers.