Google seems to assume that web sites are aimed at the country in which the adsense account address is in.
For example, you cannot use adsense for mobile or category filtering if you live in the "wrong" country. You have to live in a country where it works, not get traffic from one.
There are also peculiarities in how countries are treated. India is treated as English speaking and gets category filtering. Sri Lanka does not.
Does this imply some suspicion of sites that get a lot of traffic from other countries? Its the only reason I can think if for doing it this way.
This might also have implications for webmasters moving from one country to another, who have existing sites aimed at where they live now.
