Nearly all AWS services are regional in scope, and for many (if not most) services, they are scaled at a cellular level within a region. Accounts are assigned to specific cells within that region.

There are very, very few services that are global in scope, and it is strongly discouraged to create cross-regional dependencies -- not just as applied to our customers, but to ourselves as well. IAM and Route 53 are notable exceptions, but they offer read replicas in every region and are eventually consistent: if the primary region has a failure, you might not be able to make changes to your configuration, but the other regions will operate on read-only replicas.

This incident was regional in scope: us-east-1 was the only impacted region. As far as I know, no other region was impacted by this event. So customers operating in other regions were largely unaffected. (If you know otherwise, please correct me.)

As a Solutions Architect, I regularly warn customers that running in multiple Availability Zones is not enough. Availability Zones protect you from many kinds of physical infrastructure failures, but not necessarily from regional service failures. So it is super important to run in multiple regions as well: not necessarily active-active, but at least in a standby mode (i.e. "pilot light") so that customers can shed traffic from the failing region and continue to run their workloads.