It matters if you don't live in one of those countries because then, you just have to make sure that the Amazon store you choose ships to your country. It will also impact the costs of items for shipping outside of that country. That's really the only things that matters though when choosing which Amazon store you want your gift card for. I know that the United States Amazon ships to many countries.
It's different for each product. Take a few items and verify their prices. Germany tends to be a bit more expensive sometimes. The UK appliances will come with UK cords, importing from the US can be expensive and most is 110 volts there, with US cords. France and the UK don't always send to your country.