I've replaced 6 laptop keyboards on machines I've used ranging from consumer HP and Acer to a number of Thinkpads and most recently a Macbook Air. Some of them I replaced just because I wanted a different layout, others because they were worn out or broken. The Macbook Air keyboard was - of course - in the latter category as all these things seem to end up doing with the Q to O keys going A.W.O.L due to what I consider to be a design problem. Needless to say that the Apple machine was the hardest to fix due to the repair-hostile design. What is a quick 4-minuted job on a Thinkpad - a device known for having good keyboards - is a several hour slog on one of those Apple trinkets involving nail clippers to remove half of the rivets which did not come out of the frame because their heads ripped off. Keyboards are wear items and should be user-replaceable but that does not fit with the Fruit Factory Philosophy which instead insists on replacing the whole top shell. I go this Macbook Air for free because its keyboard had failed so maybe I should thank the FF for furthering the cause of the throwaway consumer society but there is no question here that these devices are designed to live just long enough and no longer and that they often fail on the wrong side of that lifetime.

Short: keyboards fail, quite often. They are wear items which should be user replaceable.