Rear brake is placed on the chainstays - removing the brakes from seat stays reduces wind drag.
Seat stays are not starined with brake´s force - thye can be designed much more thinner, which saves weight and increases riding comfort.
gLike
Superior Road Team Issue 2014

Carbon road bicycle issued for season 2014. Rear brake is hidden below the bottom bracket - main advantage is wind drag and weigth reduction and increased riding comfort and smoother look.

Vojtech Sojka
Bicycle and product designer Brno, Czech Republic