Most of that is true, up to a point.  It is not all true absolutely, however.  There most certainly are economies gained by taking fertilizer up the supply chain a step or two, and by taking grain down the supply chain a step or two or even farther.  The grain enterprise shares labor very well with the farm, as the grain merchandizing and transportation really starts when the farming is done, and the transportation can be done with the same assets and personel who are required for harvest to work.  The fertilizer fits well with the grain, because generally speaking you can send grain out and get fertilizer in on the same trucks and the same trips, keeping the trucks running loaded both directions.  You also remove considerable overhead from the process by not having the commodities changing ownership and being handled so many times for no reason.