OK, then it must be either some weird load balancing ruling out some people on god-only-know what criteria or just really low performance servers. The truth is that when an update is issued - people form all around the world start their downloads. If you add just 1 single server to it (1 location) the result is predictable: not enough bandwidth to serve all or just not enough computing power for the server.
Imagine only 100 000 people downloading the updated content with 10 Mbps download speed. This give you 1 000 000 Mbps required bandwidth = 1000 Gbps which is already quite a lot and I bet even more downloads take place when an update is out.