I don't think so, if just like what you said, why there are so many websites that is targeting the China, India, Chile, and etc.. and they are using Adsense to monetize their site..
Clicks from USA are generally paid better due to better conversion for advertisers. Sometimes 10 times better. Although it's possible that there are some niches for which this is not valid.
you make more on a click if their form the US,duh. the united states is not the only country that advertisers are willing to spend money on. let me think...there is canada. seriously,there are other countries that advertisers will pay for traffic other then north america. the UK,australia,europe,antarctica,nova scotia....
Yes a click from USA will be worth more then a click from Africa for example as the African are poor and unlikely to buy anything online.
Well even me I treated US traffic as premium for its conversion rate and for sure google has no reason not to treat US traffic as premium too. So in my own opinion US traffic clicks has a high price.
Usually the US traffic is paid a lot better even than the traffic coming from some of the richest countries in Europe.
I also think that is true. Some of my sites before get higher % in traffic from the US and high pay per clicks.
The high return per click from the USA is because Americans are the most comfortable with spending money online. So they convert at a higher rate and spend more when they do.