On my Madone it was definitely a case of chainring wear. Before it met an untimely demise, I had been hoping to squeeze one more season out of the 7800 chainrings.
As for it happening on the S5, that is most likely a result of the learning curve of a new gruppo (Red) and using a compact for the first time. Knock wood, it hasn't happened in a long time. And previous to the few times it happened this year was years ago before I got the 7800 and had worn down the chainrings on the stock Bontrager crank I had.
I've read about pro teams using chain catchers. I don't recall having seen one, but I'm assuming they'd prevent the chain from hitting the frame?
Jens Voigt doesn't complain about what suffering does to him, but suffering constantly complains about getting picked on by Jens Voigt.