This article explains how the 3000 mile oil change got started by fathers and mechanics as a tradition.  These two groups were very influential and passed down the idea to maintain your vehicle the oil should be changed every 3000 miles.  Then synthetic motor oil came along and significantly changed this theory.

Amsoil 100% Synthetic Series Motor provides 75% more protection against horsepower loss than required by industry standard, 72% more protection against heat that can cause major problems with turbo chargers and the 3000 mile oil change is as dated as the rotary telephone.