Do you have any idea how many people run master/slave mysql? That's async and will definitely give you data drift over time. There's an entire suite of Percona tools to detect and repair broken mysql datasets because mysql breaks data so often due to replication problems.

The world is much more async and much less consistent than anybody realizes (cash machines are even async), but everything still works pretty much okay. The last line of defense for solving irreconcilable consistency problems is customer service.