>> you need one of the other Alexa products to order it.
It likely that DOT uses the Echo as a parent device to do all processing of things like sending the voice requests to the servers and back and the DOT just works as a microphone slave device with some basic synchronization to determine which device heard the wakeword first. If DOT hears it first it sends the voice data to Echo and Echo does it's normal thing and sends the response back to DOT. (At least that was the intent when I worked on early versions of the project.)
