Perhaps you misread/misinterpreted the level of isolation that AZs provided. AZs are physically separate data centers. They are protected from fires, flooding,

Perhaps you misread/misinterpreted the level of isolation that AZs provided. AZs are physically separate data centers. They are protected from fires, flooding, physical disasters. BUT they do share some common components which allow you to do things like shift EIPs between AZs, snapshots, security groups, etc. (Source: http://aws.amazon.com/ec2/faqs/#How_isolated_are_Availability_Zones_from_one_another http://aws.amazon.com/ec2/faqs/#How_isolated_are_Availabilit...) Regions on the other hand, are completely separate installations of every component of the AWS stack. You can verify this because no resources can be shared between Regions (snapshots, groups, EIPs etc). You can also verify this during an outage. IE: When the US-EAST-1 API becomes unresponsive (due to throttling), the US-WEST-1/2 are still available.