If you're like me, you run multiple browsers; FireFox, Safari, Camino, and (last, and certainly least) Internet Explorer... actually, all three of the past versions of IE: 6, 7 and 8. And, if you have any ability to see, you'll notice that there are aspects of the site that look different—most notably the navigation buttons, the sidebar sections, and certain other elements.
The reason for this has to do with a principle embraced by those interested in making the web a better place:
progressive enhancement graceful degredation [see comments below]. Basically, what this means is we develop the best website we can, and make it look great in the most standard and open way possible, and accept that the website might not look as good in older/less-compliant web browsers.
If you open the website in Safari (or any other standards-compliant browser!), here's what you'll see: