Yes. To play from North America you must purchase a North American copy of the game. To play from Europe you must purchase a European copy of the game. Note that this restriction impacts where you can play from, not which game worlds you can choose to play on.
By purchasing the correct copy of the game, you're supporting the game in your country, and you'll be connecting to your local data center, using your local customer support team, and downloading the correct language support for your country.
Here are some answers and clarifications for you! First, if you purchase the game from https://buy.guildwars2.com/ you'll automatically be sorted into the right region.
And don't worry -- we want you to play with your friends wherever you are. This policy only affects where you can login from -- not which worlds you can access. People from NA will be able to play with people from EU at launch. We've got two datacenters -- one in NA and one in EU. Those who do not fall into either of those two regions will default to the NA datacenter.
