...Frogboy is a big believer in free markets. The idea being that the government (your Sovereign) makes an initial investment (the Caravan unit) and then once it arrives "private industry" takes over and somehow generates extra resources out of "nowhere" (presumably by making the whole process more efficient and cost effective than the government can by itself). Whether or not that is valid economic theory I leave for you to decide, but it goes to show how Stardock games are actually subversive training programs for Rebuplican/Conservative economic policy...
Here's another take -- you have the rich-in-food freely giving to the poor-in-food, sharing their resources for free (as there is no 'tax' or 'cost' generated when the poor-in-food get the food). Thus this is a socialistic, perhaps even communistic, system! 
A capitalistic system would charge the poor for the food (ie it would cost gold to caravan food), and the price would vary according to:
-the demand for food in the food-poor city (ie the gap between the food-poor cities' local food production and their pop)
-food supply in the food-rich city