Centralized management does not mean centralized infrastructure. Any of these systems could distribute the APIs and message delivery infra across multiple independent jurisdictions, regions, and providers, and do clientside load balancing.
The fact that these systems are centralized in management does not mean that they need to have any SPOFs.
Also, the Apple App Store and iOS activation servers are the biggest SPOFs of all. Without them, even with a brand new working device, you can't activate it or install apps to communicate.