My friend owns asuli0.wordpress.com which is a very popular Spanish Club Penguin site. Most of the traffic is from Mexico though. His competitor, clubpenguinaccess.com, which is also popular, makes about $60 a month from adsense -- and I believe it is because they have Mexican visitors, and advertisers pay less. Now, an english speaking Club Penguin site, ClubPenguinCP.com, makes around $3000 a month from Google adsense. So.... I take it that US, Canada, and British ads pay more? What about Australia or other countries? I can see that there is less income from ads clicked within Mexico.
It's not about where the user is from (directly), it's about the value of the traffic. If your site gets visitors that tend to not spend money (with the advertisers), the value goes down (AdWords advertisers aren't going to spend a lot per click when the traffic doesn't convert).