This is actually untrue. Multiple Nest Thermostats do actually interact, although Nest doesn't really make it clear to what extent. One function, for example, is the Away function. Setting one device to Away (or having Auto Away trigger) is communicated to other devices. When the Away is deactivated - manually or automatically - it also does so on the other thermostats. The new Nest Protect (CO2 and smoke alarm) also interacts with Nest Thermostats.