I read the parent comment as questioning the wisdom of relying on a cloud provider (but not specifically AWS, as you indicated) for a global operation life FedEx. Even with service zoning, in extreme cases that provider constitutes a potential single point of failure. Unless FedEx are able to run their core systems on Azure and Oracle‡ then I think the point stands.

It would be interesting to know how Fedex sees the risk/reward equation, and how Azure (for example) compares to a (IBM?) mainframe data centre in terms of reliability and uptime

‡ I'm not sure if there are any cloud neutrality solutions that permit this, but it is possible that FedEx have rolled their own.