I've met a few americans, some of my relatives are american, and although they're pretty smart, they're not the...ahem...thinest of people. Although on the whole they're pretty nice to be around, the average american knowledge of the wider world is somewhat limited.
Going on from the whole fat thing, me and a friend tried to figure the ratio of hot women in america (admitedly when drunk).
60% ish of americans + are overweight/obese. only 50% of those who are at a normal weight (ignoring those underweight, since i don't know the numbers) are women.
We now have 20% of americans being normal weight women. Due to an ageing population probably only 40-50% of those are going to be what can considered a (for a generic young male) 'hot' age, i.e. 18-30, for overt hotness (and legality).
So far, we have about 10% of the american population, then considered that probably only 50% of those are going to be good looking. So, only 5% of the american population, at an estimate, are hot females.
It would explain why i keep seeing the same women come up in porn shoots all the time though...
For some numbers, at a rough population of 300,000,000, and a country size of 3,710,000 sq mi (rounded numbers), that gives 4 hot women per square mile. There are endangered newts with larger numbers than that.