I actually do charge my laptop battery to 80% most of the time (100% when I'm traveling though). I might do the same with my cell phone if I had a configuration option that allowed me to say "stop charging at 80%. But my cell phone's battery is replaceable and a few orders of magnitude less expensive than my traction battery. I also don't expect it to last for 10 years or more.
I read a (non authoritative) article recently that suggested that electric car manufacturers design the BMS to initially charge a brand new battery to 80% and then, as the battery deteriorates over time, to increase the charge so that the consumer sees a consistent value on the range reported by the instrument cluster for a "fully charged" battery. Of course, that only works until even a 100% charge isn't sufficient to maintain the expected range because of deterioration.
I've also read that 100% isn't especially bad in cool temps, compared to 100% in hot summertime temps (depending on how hot your summertime gets). I actually prefer to keep my PHEV charged close to full in winter (as opposed to fully depleting it all the time, because that's not good for it either), but when July rolls around, I'm probably going to be looking for a way to limit the charge to less than 100%. Currently, there's no easy way to configure the charging system to stop short of 100%. You can program it to stop at a certain time of day, but that might be hard to translate into a certain state of charge, unless you always start at a certain state of charge and you always plug in at the same time every day.
As owners of cars that use a battery with a finite life and expensive replacement cost, we're confronted with a dilemma: do we go out of our way to baby the battery in order to prolong its life? Or do we use it in a way that is consistent with the owner's manual's guidance, and with no additional precautions, on the hope that if its going to wear out while we own our cars, we want it to wear out while it's still under warranty? I don't know the answer to that one, but I'm tempted to baby it within limits of what's practical/convenient for me personally.
2018 Niro PHEV Gravity Blue