Ultimately, it's all about the odds. That's what HA, replication, and DR are all about. It's so statistically unlikely for certain things to happen, they just fall out of the realm of reason. Most operations folk I've talked to don't even consider their disaster recovery plans to be within the realm of feasibility. The chances of a catastrophic event rendering the owners of the system defunct is many orders of magnitude more likely than an event that breaks the standard data fail-safes that most datacenters have in place.