I recall an interview with someone about this - I think it was Tim O'Reilly - where it turned out that Bezos had a hard time getting the developers to even see the value in it. They kept putting in confirmation dialogs and he'd have to go back and tell them to take the confirmation out, and that was what persuaded O'Reilly it really was innovative, the fact that it was difficult to get the programmers of the feature to even understand the requirement.

Edit: maybe not O'Reilly, since he penned this [1]. Maybe it was Kevin Kelly?

[1] https://www.oreilly.com/pub/pr/537