But what about 'Gob Bless America'? I'm pretty sure Mexico doesn't give a shit, i can't imagine Canadians saying it, and i sure as hell can't imagine people in the US saying it meaning those other non-US countries...
When people all over the world complain about Americans, they really don't mean Mexico, Canada, Jamaica, Cuba or any of South America...
Here's a question; people from France are French, people from Spain are Spanish, and people from Mexico are Mexicans. If citizens of the USA arent called 'Americans', then what are they called? 'USA-ians'?
People who could not name the country after something sensible. (troll mode)
Now more serious:
In Spanish they are often called "Estadounidenes" (Estados Unidos is the name of the country, so effectively Unitedstatians as you propose). This is mostly because of the influence both ways between Spain and Latin America. Or you could say "people from the US". I have American family, they are from Argentina.
It is like calling Europeans only those from the EU, forgetting about Eastern Europe, Norway, Switzerland,the Balcan countries, etc; like calling Arabs only those people from the United Arab emirates, just because it has Arab in its name.
So the smart thing would be to try and change it, but hey, part of this comes from things that arise in the video NuberT posted. Ignorance, unwillingness to change and adapt (curious how the same happens in cRPG with class balance and QQing), being mislead by media, official people, etc.