Chandoraa: ..."the Americas" to refer to the American continent as a whole, rather than "America" (which they use to refer to just their country). So yeah...
Trilarion: But this is also kind of misleading or not unique usage then, isn't it. So there is a continent, the American continent and it is called the Americas because it consists of two parts and in the North American part there is a country which calls itself America and the inhabitants of this country are Americans but all the other inhabitants of the Americas are not Americans then, otherwise how could you distinguish them from the other Americans who live in the Americas?
From the name of the country USA the correct name should probably be US Americans, because the citizens of the US are Americans but specifically the Americans of the United States of America and not of any other State of America. But people are lazy and forget to add the US and then it becomes a bit messy. So just a laziness effect, the correct name exists.
North America and South America are not the same continent though, thus "the Americas" rather than "America".