Its not responsive in it current definition. The site is just fluid (based on percentages), the reason some elements seem to realign/behave like responsive design, is because those elements have fixed widths.

History lesson: Fluid widths were quite common until around 2005, as there weren't a large number of resolutions to cater to. Around the start of 2006 designers started switching to 800-960px to have the webpages look the same or nearly the same on every page.

[0] http://www.w3schools.com/browsers/browsers_display.asp - In early 2006 77% of displays were between 800-1024px wide.