Amazon.com does run on EC2. You can bet that if EC2 had a a complete regional outage (which is extremely rare) Amazon.com would be down.
In general Amazon.com makes extensive use of AWS services internally as well, but it's very well architected to handle service outages without it being immediately obvious to the end user.
In general Amazon.com makes extensive use of AWS services internally as well, but it's very well architected to handle service outages without it being immediately obvious to the end user.