Especially if you're in Europe (I get a ping time of 24 msec from Switzerland), the pages load nearly instantly. It's actually the sort of thing that you notice and go "whoa" it's so fast.
Yet there's nothing special about it. It's just a regular web server, written in D, that serves pages really fast (probably out of cache).
If you use HTTP caching and compression appropriately, and keep your design light, there's no particular reason you need to use Javascript to speed things up.
I'm not saying non-single-page-apps are slow, but that single-page apps can be faster in certain circumstances. When I click a link in your example I still get that slight delay, which could be eliminated with a single-page application.
