There are two separate things here, which I think are getting smooshed together as one thing and getting confused.
I would bet that there really isn't that much difference in the physical status and energy storage of those two batteries. But the software of the Battery Management System that uses algorithms to try to read the amount of energy? That can get confused and out of sync pretty easily with certain things people do with their charging and how they leave the state of charge. A lot of that comes down to "visibility".
If a car is left sitting at almost the same state of charge all the time, like your 80% case you mentioned, the system's estimation doesn't have much variation of voltage to look at. It looks the same all the time, and the estimate drifts more and seems to lose a significant amount of energy. A battery that gets exercised more, to go to high and low states of charge, lets the car's software "see" the high and low ends and kind of does more of a "true up" to tune that estimate in more accurately on a pretty regular basis.
So I would say that while the 10% to 90% behavior is harder on the car and probably slightly more damaging, it's simply keeping the estimate more accurate. The constant 80% is generally healthier, but is getting a very fuzzy estimate, which isn't really a bad thing for the car; it just makes owners really uncomfortable.