I think they mean that it reduces the complexity that a single developer has to deal with.
Amazon abstracts complexity away by having someone else deal with it. Big difference. One would imagine software progressing towards abstractions that are simpler and allow one person to do more, what we are getting is instead abstractions that only make it seem this way when in reality it's going in another direction.
Complexity is increasing to the point where one person can do less, but companies like amazon don't let you realize this by hiding the true complexity behind other people who deal with it.