I would imagine most advertisers limit ads to be displayed mainly for North American, Australian and European users. What if my site has a higher than average number of Asian users, would there be less ads shown? And ads with a lower PPC?
Yep, I think that's the idea. The way to know it for sure is to find an asian open proxy, load your page through it and see what happens.
Why don't you just use the adsense preview tool? https://www.google.com/support/adsense/bin/topic.py?topic=160&ctx=en:leftnav
Maybe because not many Asian countries are on the geo-target list in the preview tool (only Japan, HK, Philippines)