USA = United States of America. I.e. States north of Mexico and Alaska and Hawaii, not Canada.
American = citizen of a nation in Americas. Apparently even Hawaii includes in Americas, which doesn't make sense to me... It's an island(s) some 4000km away from the continent That's like Finland being included in to North Africa, the distance is shorter than that of Hawaii and the continent.
That's because USAian or United States of American doesn't roll from the tongue so easily as "American". Same thing with Spain and Spaniard meaning a citizen of Spain.
So, you and the wiki are correct that that's what the word means in 99,999...% of cases. No Canadian, Mexican, Brazilian or any other citizen of South America would ever call them shelf American, the word's tainted
Of course you do... You fail - you pay. And they have to transport your body... That's petrol expenses, and also since you're adding an additional weight to the vehicle, even more petrol is used.
And it could get even worse if the vehicle is old and not burning the fuel efficiently...