Legal Question in Technology Law in Indiana

Each country has its own set of laws. Amazon probably sees a legal issue with allowing this type of download in Japan. (Perhaps Japan restricts access to some types of material. It's also possible that there are copyright or licensing issues. Another possibility is that a different company has exclusive Japanese distribution rights for these videos.) If so, the company is not locking you out personally. It's just applying the same standards to you as to everyone else in that country.

My guess is that you are not actually locked out of the videos you purchased. You can probably still download them in the U.S. You might be able to do so in other countries, too. But your downloads are subject to the laws of whatever country you're in at the time. Amazon has to abide by those laws, even if they are very different from the laws that governed your purchase.

You should look at your Amazon user agreement and the agreements for these particular purchases. They may explain that you are only allowed to download the files in the U.S. and/or explain other restrictions which are now preventing you from accessing them.

You ask why this is any different from watching the DVDs and downloaded files you brought to Japan with you. One difference is that preventing a download is much, much easier than remotely disabling a DVD or other digital recording. Another is that your licenses to those recordings probably do not restrict your right to take them with you when you move. The most likely explanation, though, is that the act of downloading a recording raises legal issues that are not raised by watching a recording you already possess.

Whether the company's actions are legal depends more on the laws of Japan than of the U.S. It may well be that Japanese law requires Amazon to do what it's doing.