I dunno. Maybe this is true for off-road bikes, but I have basically never done any maintainance on my (numerous) cable-pull systems after they get through the cable stretch phase.
My old 9-speed bike is rock solid, but I ride it rarely (utility purposes, basically).
My 11-speed mechanical bike needed adjustment probably 3-4 times a year (and on one of those occasions it'd be time to swap out the cables). Until I upgraded the shifters would eventually "eat" cables (well, on the right side anyway) and strand me in the lowest cog (Ultegra 6800), which was a huge hassle.
My 11-speed eTap bike asks only that I charge the batteries periodically. In the 2 years I've had eTap on that bike, I've spent MUCH less time futzing with the drivetrain than I did when it was mechanical Red, or than I did when I rode the Ultegra bike full time.
It says that cable-pull systems require more (and more intense) maintenance than electronic systems do.