When I worked for a loan processor, they were quite happy running over $100k/hr revenue through a single instance of PostgreSQL. There were slaves to offload analytic and report loads but all transactions went through a "SPOF" and we just manned up to keep that database running. Don't tell me "real apps" are all that redundant and bullet-proof. Designing and operating redundant infrastructure is much harder and costlier than most make it out to be.