While what you say was certainly true when AWS launched, today it is not. Much of Amazon is hosted in an EC2 VPC connected to the traditional prod network. This includes all of retail website and (today) many of the services that power said website.
Other AWS services are also used frequently and heavily. AWS use is strongly encouraged for any new projects.
> "I also wanted to clarify that Route 53 is an Amazon-built and operated service. It is not a re-branding of a third party DNS service. Over time you'll see various parts of Amazon move over to use Route 53."