I see this question pop up some time here. I am located in the US and I am wondering. What made me curious is that I placed one of my blogs on a DoFollow Comment list and I get 10-12 hits a day from India/Pakistan. None of these people have ever clicked an ad on my site so I don't know if the pay for their click would be very low, but I think that's the concern.
In my opinion CTR is not the concern, but the conversion is. Also, clicks generated from these countries on Adsense ads have a higher CPC.