Why do Asian savory recipes call for a few pinches of sugar?
First, there are plenty of sour ingredients in Asian cooking, that are de-acidified by a little sugar. Tomato paste, peppers and soy are examples that come to mind.

Second, and this is the Zen-style answer, is that the sugar is to sweeten the dish a little. One teaspoon of sugar in a sauce is plenty sweet enough, especially if you're not used to having 6tsp of sugar in a can of Coke daily. Sweetness, like saltiness and spicyness, is something we get used to easily.