The r pi acts as a controller for the miner. Most miners are just a array ofchips (asics) and requires a computer of some sort. You could plug the Black Arrow/KNC and others, in o a regular pc and do the same. But you would be wasting power. They choose a Rpi or Beagle Bone, the Avalon basically has a router with modified firmware to run Cgminer, since they require very little power. I run my Pi on a old cell phone charger. Some gear like the Asic Miner blade have an on board processor and network interface and dont require a computer.
