I have been trying to search for the full legalese that explains this but I haven't been able to find it yet. The bottom line is that your credit card must be registered to an address in the country in which you want to purchase the content.
If you want to call it an "Apple thing" you can, but the reason that Apple does this is because not all content is legally available in every country in the world so if a person is trying to circumvent that legality by purchasing from another country, this "Apple thing" might prevent one from doing that. Apple may not be licensed to sell music in all countries, or certain apps (for instance FaceTime in Dubai) in all countries - whether it has to do with the vendors' licensing and copyright restrictions - or government restrictions.
And yes, even free apps would come under these terms. Apps like Pandora Radio and Netfilx are only available in certain countries - IIRC. Using your credit card to purchase an online subscription is based on whatever the terms are for that particular vendor.