AFAIK, the Amazon download puts exactly the same files on your hard drive that you get when you buy the DVD. It is not the same as Steam, or similar systems, that do not allow you to install an executable copy of the game, but instead provide a unexecutable file that can only be used after it is modified by a runtime patch from the Steam website. You can back up the Amazon install package to removable media and save it. That is a HUGE difference.
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