That's not really true. With a single, non-replicated server, you're also very much exposed to network failures. If the server's connection goes down, you're screwed. Compare this to a Google replication setup of 2 East Cost, 2 West Coast, and 1 central USA server. The client must only be able to reach two out of three data centers (and they have to be able to communicate with each other). That sounds much more resilient to me - and I guess Google agrees, since they deploy the setup.