A device would only need a camera to receive information, and yes, at the point you need bidirectional transfer, I'd concede that this isn't the best method.

However, adding a small lcd display allows the presentation of human readable data as well, and many devices already have screens on them.

(I always thought serial over TRS (headphone) cable would be an interesting option as well.)

Less robust and cheaper

Bluetooth LE is very robust. Much more so than a camera and screen.