Or any active content! Why would Amazon sell apps in only North America?!

It's called geoblocking. The Australian Senate held hearings into it. Fun fact: I was looking to buy Cowboy Bebop and Star Trek: The Next Generation on iTunes. Not available, but definitely available in the U.S. App Store.

Even before streaming, the media publishing industries have been into segmenting the world into different markets for the same product: For example: books separately published in the US and the UK, DVDs and Blu-Ray disks with region codes that prevent playing on the other region players (providing they're players which obey this flag.)

Time to disrupt these arseholes.

But unlike most other media there's no other way to purchase them. I can't buy DVDs of Kindle active content, I can't get it off ebay.

I guess they mustn't consider the international market worth the trouble of solving whatever legal issue is stopping them from selling them to other countries.