I've heard this before and am still puzzled by it. I've been using Apple devices for over a decade, and only ever had one or two phone charger cables fray, but they were really heavily used and looked like they were used in a farm for months. The vast majority still looks perfectly fine. I guess there must be small habits that have a great effect on degradation. Like stowing away the charger after every use vs keeping it in place at a desk, for example.