It is a narrow application of general purpose machine learning approaches. Convolutional neural networks, supervised/reinforcement learning are not limited to Go. They've found success in a variety of applications.

And while those applications are narrow, they're significant progress in a short period of time.

In this game from only 4 years ago you could see one of the state of the art bots getting humilliated by an anonymous professional player: http://gosensations.com/?id=2&server_id=1&new_id=1392