When I look at my (investment related) site from an South Asian IP address I see LOTS of ads for Facebook. I see vyry few when I use a UK IP. I have seen the same on other sites.
It may just be that Facebook is one of the few advertisers advertising globally, so their ads show where Adsense rates are low, rather than that they are targeting the region.
That still leaves me asking why. I suspect a desperation to be sure user numbers keep growing until those who have agreed not to sell immediately post-IPO (Facebook as a shorter period than most for this) get a change to sell.