It's not less noticeable. It's unnoticeable to anyone who isn't a professional mechanic.

How many people complain that their new car is slowing down significantly after less than a year, or becomes inexplicably unusable around the time the year+1 model appears?

This is very much not the case with the iPhone slowdown, where a lot of people were noticing issues, on a product which already has a pitiful and barely practical battery life.