I think the answer is more or less that transportation costs aren't going down. We produce more than enough food to feed the entire world population, but the poor can't afford to buy it because of the cost of transporting it to them.
This doesn't seem right to me. Transportation costs are negligible for all sorts of products. It costs more in gasoline for you to drive to your local Best Buy and bring home a DVD player than it does to ship that DVD player from the factory in East Asia somewhere halfway across the planet to the store. Huge economies of scale have been realized in transportation.
If, on the other hand, we include under "transportation costs" the costs of dealing with corrupt governments in many countries who enrich themselves at the expense of their people, then yes, there are significant transportation costs in getting food to poor people in many countries.
