Brake cables are usually spiral wrapped, because in theory, under load it could force its way between two of the longitudinal strands, if those were used (like in gear cables). I have no idea if it is a thing though
Edit: ah, as usual, Sheldon has the answer http://sheldonbrown.com/cables.html
(this probably predates modern compresionless brake cables though)
Ok. Lazy googling suggests brake housing has some extra layer (in this case kevlar) that must be enough reinforcement compared to regular gear cable housing... can't see how they'd get away selling it if it did split regularly...
Brake cables are usually spiral wrapped, because in theory, under load it could force its way between two of the longitudinal strands, if those were used (like in gear cables). I have no idea if it is a thing though
Edit: ah, as usual, Sheldon has the answer
http://sheldonbrown.com/cables.html
(this probably predates modern compresionless brake cables though)