Is the human collarbone supposed to break?
This looks like a misinterpretation. Because collarbone is the only horizontal long bone of the human body [1], it is the first to fracture when falling on the shoulder.

Its fracture can affect many structures:


  The muscles involved in clavicle fractures include the deltoid, trapezius, subclavius, sternocleidomastoid, sternohyoid and pectoralis major muscles. The ligaments involved include the Conoid ligament and Trapezoid ligament [1].


It is indeed a shock absorber, but for the upper torso (some way or another any bone can be considered a shock absorber):


  The clavicle also serves as something of a "shock-absorber" for the upper torso. Physical contact from the side will be partially absorbed by the clavicle. Because of this function, the clavicle is a very commonly broken bone [2].


The fracture can lead to severe injuries:


  Displaced or comminuted clavicle fractures are associated with complications such as subclavian vessels injury, hemopneumothorax, brachial plexus paresis [...] [3]




References:


Wikipedia contributors, "Clavicle fracture," Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/w/index.php?title=Clavicle_fracture&amp;oldid=615723256 (accessed July 30, 2014).
Erich Rosenberger M.D. Anatomy And Physiology (2009). Available from http://www.sciences360.com/index.php/anatomy-physiology-299-12859/ (accessed 30.07.2014)
George Mouzopoulos, Emmanuil Morakis, Michalis Stamatakos, Mathaios Tzurbakis. Complications Associated With Clavicular Fracture. Orthopaedic Nursing, October 2009, Volume 28, Number 5, Pages 217 - 224 - See more at: http://www.nursingcenter.com/lnc/cearticle?tid=938803#sthash.F09wonvJ.dpuf