OK, that makes more sense. Actually reading the site, I don't see why anyone would opt for that service over something like CloudFront and some manual optimization, unless it was a very small project.
CDN's are popular for static content, but there are a number of very good reasons to proxy dynamic content through your CDN as well. The most obvious advantage is that you can terminate the TCP connection much closer to the user, and then can leverage the optimized backhaul network to fetch from origin. This alone can be a huge win, especially if you have SSL in the mix, which requires 2-3 RTT's before it can even send the request.