I just have to ask, I've had an issue with Amazon in the past where I've signed up with them to get something I specifically wanted but wasn't informed until after the fact that what I wanted wasn't available 'in my region'. How good is Amazon for (pretty much mp3) purchases these days? I'm assuming that because the link is there it must be pretty reasonable now. Also I'm partly asking because Ubuntu now comes with a link to Amazon on the sidebar now by default and apparently it works with Ubuntu One pretty well too.
For digital content Amazon still enforces region locking. For goods they send some overseas (Kindle, Kindle Paperwhite, memory, HDD, shoes, cameras) and some you need a service like YouShop for NZ delivery (Kindle Fire, other electronic devices).
I'd say mp3 falls in the same category as movies so they're probably restricted to the USA.