My guess is that there is shrinking number of presidents/ceos.
CEO wise, in less than 2 month, in WG, it went from about 450-500 CEOs to around 300 now, that is between 30-40% decrease.
Before starting all those fancy space shuttle stuff, which is basically made for vets who are bored with the current game, i think there is a need for new players to step in and takeover the countries left.
Lots of other games provides some kind of referal link, and i think it simply works well. Any full member should be able to refer somebody else and get for example 1 GC for every 30 GC(1 month subscription for an empire) a person spends.