I just looked through quickly, but it appeared that the segment with the most companies in the list is insurance... I guess Warren Buffet is still right...
Just adding up Vitol, Transfigura, Cargill and Koch Industries you get to 665B in revenues.
Commodities trading is a behemoth, everything that surrounds us had to be mined and refined at some point, and most of it comes from very far, way beyond a 10-mile radius, thus prompting the need to move commodities around.