There's nothing stopping you from using a traditional CDN vendor as an application CDN. I spoke to the folks at Edgecast about this a year or two ago, and they didn't have a problem with it. However, it sounds like Amazon made some specific optimizations for application content which could be more appealing.
Also, CloudFlare offers the same service, but with added security and anti-spam features.
Also, CloudFlare offers the same service, but with added security and anti-spam features.