@smeffw: As with all products released across borders prices generally have to do with licensing, tariffs and the market they are selling to. It's why Netflix can only serve certain content to each country and why they have to pay content creators again each time they want to release it to a new country.
After that you have to deal with each retailer's promotional deals with the distributor on a per country basis. Bigger markets can make bigger numbers so they often get a better deal. Perhaps the EU's "borderless" nature can allow a better deal to companies there or perhaps their market doesn't support that price point while the US market does? It can get rather complex when dealing with so many varied factors.
TLDR: It's complicated and governments/laws become involved. The only real way to change the market is to have a true boycott on price which is impossible in a country with so much wealth.