Another figment of thought on the previous topic: There is also always the matter of the environment of a fictive world being not necessarily identical to that of Earth (and even Earth varied by region quite a lot). Say, if your medieval world has priests who can [i]actually[/i] summon and dismiss rain at will, then I'd say it is quite safe to claim that crop dearth due to either too little or too much water is a significantly less common occurrence (as is the starvation that'd otherwise come with it).