Well your experience is maybe more based on your friend behavior than on an absolute rule.

This is the same for absolutely every manufactured goods. The same durable car model will be kept for over a decade by some people while some other opt for a leasing plan that guarantee a new car every two years. But the intrinsic quality of the car remain unaffected.

To ponder this you must consider what become of the phone they replace : did they trash it or did they have a second life with a less edgy owner?