Just another bell and another whistle.
Except in really hard water areas, I would bet most housewives ignored the rinse-agent issue entirely, as did me sainted Mother. I remember, clearly, filling the Rinse-Agent dispenser on our GE Pull-Out the time she first used it with the little glass bottle that came with the machine, seeing the dipstick and having that explained to me, and then, never again.
NYC had soft water (actually, it's the best municipal water in the country; piped 90 miles in from the Ashokan Reservoir) and if there had been a spot on her everyday glasses, she wouldn't have been bothered with it. She hand washed and dried all the good stuff. For me, it's another nifty little gimcrack that needs to be figured out and played with. Local water here in CT is also soft and I can't tell the difference when the rinse dispenser runs dry; that's one reason I think gauges and dipsticks are useful. Also, I will never buy Rinse Agent that ISN'T dyed a bright color again--you need to be able to see it.
I think it's pretty comical how Madison Avenue still makes a fuss over spots on glasses; as if anybody but the Royals and Hyacinth really cared.