Not surprising. The equator runs under the bulk of Africa, through the middle of Brazil and Indonesia. The Southern Hemisphere ends up containing about 80% water, about half the landmass of the Northern Hemisphere. And about half of the Southern Hemisphere's landmass is uninhabitable Australian or Antarctic desert.
The more impressive fact is that half of the world's population lives in a small-ish circle in Asia: http://io9.gizmodo.com/more-than-half-of-the-worlds-populati...