This is not true in developing countries. From my experience, the poorer a country, the more likely you are to see extensive, serious use of Facebook. And the revenue growth opportunity is huge for FB in these places. It is already flat or slightly negative in highly advanced countries.
Kind of, but GDP per capita is way lower. It would take 35 average Nigerian users to replace one average American. Which still isn't exactly true, since there are high-margin items that are impossible to cross-sell that way. E.g. a $1k iPhone is affordable by a $70k american but not by any single $2k income Nigerian.
Sheer quantity of users doesn't replace higher GDP cohorts.
