Typical water heaters in the US are designed not to empty unless the drain valve is opened (or when the tank develops a leak just after the warranty runs out). This is by design to prevent the possibility of heating an empty tank.
From what I’ve read, in the UK they often use an indirect water heater where there is no burner in the heater. These systems will not be damaged by running dry so they are allowed to empty. If such a system is installed above the living space the pressure from the cold water inlet is not required to deliver hot water.