Many people go by the batting requirements. I do use the batting requirements as a guideline but I prefer to space the quilting so that it compliments the quilt. I took a class with Karen McTavish and she also quoted your fist size recommendation, especially for show quilts. I have also had situations where the quilt required more quilting to reinforce a few bad seams or to quilt out fullness in areas.
But many of todays battings have scrims or are needle punched in such a way that quilting can be spaced as far apart as 10".