They are not just radio. Most hubs (Vera, Smartthings, Homeseer, Wink, etc.) run software that can control various devices via many protocols using whatever radios they have installed. Some devices use Zwave (a standardized protocol at a specific frequency), Zigbee (different protocol, different frequency, not so standardized, can be proprietary), BT or wifi. The hub runs a program that can automate (not just control) many functions of the house. These hubs also work with Echo to control the devices via voice. Note that the Philips hub is very limited; it is mostly a (formerly?) proprietary radio to control Hue bulbs. The zigbee radio in the Echo Plus allows it to directly control compatible zigbee devices, and not all zigbee devices are compatible with each other.