Actually, more complicated robots tend to have multiple brains - be they multiple PCs or multiple controllers.
It is not unusual at all to have a microcontroller dedicated to a simple task, and then have it communicate with a larger, more powerful processor or microcontrolle any data it may need.
For instance, you can have one microcontroller dedicated to controlling and regulating the speed of two motors. Then have another one read sensor input and translate the data. Have a third control your camera turret, and a fourth talk to all of them and figure out what to do with the data.
