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.
I understand this wasn't a general AWS outage, AWS !== amazon.com, and that successful hosting in EC2 requires specific architectural decisions to make things run reliably in face of zone/region outages.
What i didn't realize was that jokes about Amazon being somewhat slow and cryptic with information about outages while they're happening were off-limits.
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.