It is certainly true that North Americans are more aware of what Worldcon is like than people outside the US. There's a good chance they will have been to one. But even so a Worldcon can be quite different to a local US convention. One of the interesting things about overseas Worldcons is that you tend to get committees vowing to do things "our way" instead of the "the American way", whereas in fact the ideas they wants to chuck out are more a function of the sheer size of the event than of its Americanness.