What a crock of *****
Arenanet have stated that American keys are a seperate region to EU keys.
THe links they reference to have nothing to do with the US / EU keys, those are just login issues, the region lock is only apparent if you try and use the cash store.
They have this on their facebook page.
"Anyone who thinks they received USA region version of Guild Wars 2, this is not the case. Nevertheless, contact Guild Wars 2 support and they will be happy to swap your key to an EU region key."
So is it NcSoft or GW2 Support we contact? It's a bit lame to be honest.