it seems like the answer to your question is: nobody really knows, but the phenomenon seems to be real. a simple way to see for yourself is to get your hands on a set of cables that have been used for a while and some brand new ones of the same model and switch back and forth. if you actually do get to do this, one thing to be careful of is to avoid bending, crimping, stomping etc. either cable during your switching back and forth - that might impact the comparison.
