Some cables and outers (cheap ones) will probably stretch more than others (expensive ones). There is no way a correctly set up bike should need cables adjusting on a 75 mile ride though. I've certainly gone literally years and thousands of miles without adjusting indexing on Ultegra and Dura Ace. Maybe the lower end groupsets need more maintenance?
Precisely. I've spent many years developing test protocols for stressed engineering components ( chains and cables for example ). There's a test which is done, to determine what's known as the Stress corrosion coefficient. It involves determining a number (nd) by producing what's known as a Weibull distribution graph. These are produced by subjecting a test article ( a chain or cable ) to increasing strain levels, applied at increasing rates, until failure. Once these tests are completed, and the calculations are done, the Stress corrosion coefficient (nd) can be determined. This essentially tells us how much grief you can give the tested article before it fails ( stretches irrecoverably past its elastic limit, and / or snaps) With these types of components, there are fairly defined grades / criteria into which we group production runs. cGMP or 'Gucci' as it's referred to, is high end aerospace grade stuff, which is very resilient, then we have 'Gen' this is standard construction grade stuff, and is used in lots of important things like engines, and building construction / civil engineering. Then there is 'dog sh1te', as long as the application is not safety critical, or regulated, this stuff will do. Finally we come to 'consumer' ( or 'gash' as it's known ) grade stuff. Most 'gash' finds its way into things like bicycle componentry, where it's sub divided into further categories. These are from plain old commoner garden 'gash' which equates to 'high end bike stuff', right down to 'total and utter gash', which is componentry commonly found at the BSO end of the market.