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.
@digmen, exactly the sort of lines I am thinking on.
They need growth in numbers to justify the valuation, and developed countries are saturated, but, user growth on lower income regions does not translate into the same level of revenue growth as they would get from rich country visitors.