You would typically be right. However, the saying as of 2013 was "At any given second there is always at-least one new computer being plugged in, to support S3's growth."

> Every rack that is sitting there is an opportunity cost for another efficient or more profitable rack.

If AWS wasn't already supply side constrained on new hardware to fill new AWS data centers, you would be correct. However, they do not yet need to re-use those old racks, instead they are accelerating how many new racks they are building.