One will not earn more per click however the volume of USA traffic is the highest.
I feel it is strangely co-incidental that Adsense is geared from 00.00 US time thereby allowing US advertisers to have the lowest CPC and, obviously Adsense publishers, their lowest EPC, when the supposedly "biggest" and supposedly most "competitive" market in the world, whilst advertisers budgets are running out for a Google Day.
US advertisers pay less than Europeans for equivalent Adwords keywords, I have the statistics, I am an advertiser, I know.
I'll give you these actual figures to consider my earnings over the past 2.5 years:
Last 8 hours = 33% of the day
Page impressions = 25-30% of total
Clicks = around 20% of total
Earnings = 12-15% of total
Hmmm, I'll say no more!
Yes, your mileage may vary however I am not going to bother with addendums, "my" earnings are obvious.