On the site, it says
"Please note, they are not offered in the USA to USA residents"
Is it possible that you get a different page/notice when you access the site from the US?
What it does say is that you must have been a member for six months in order to get this card: "Please note International Currency Card products are only available to existing American Express customers with more than six months of membership"
The reason that I would like to apply for this card is because I'm not a member yet.