Right you are! Like airplain chairs too.
I for one think that this is the early romance of America with cars that brought a spesific body pattern to female trunk. There is no what French call "la taille". It`s just a wide and large truncated pole, what Russians call "koloda", Russian women who for the 90% didn`t have cars and had to deal with public transport or walk with large houshold bags grew fat differently - on the belly mostly, not on their sides.
And then America started to eat huge portions and drink sweet pop-soda-drinks...