The primary purpose is what I'd call convenience wireless.  Not having to connect a cable forvery bit communication, and to gain some freedom to move around. Not too far, but certainly within the same room, and a bit beyond.

Wifi would of course be better to have, but that technology is currently inaccessible if openness is a priority and you don't have the budget of, say, Google or Apple. There is at  least one commercial WiFi offering that can be used with the Ben (closed hardware design, of course), so there would have been little point in trying to mimic that.

Besides, IEEE 802.15.4 is an interesting technology for anything that needs to be simple, which also includes DIY designs, home automation, and a lot of industrial applications.