"California launches a campaign against the widespread notion that oil changes are needed every 3,000 miles. Officials say the practice wastes millions of gallons of oil a year...."
20/20 did a story on this back in the mid 90's. With numerous tests they determined 7,500 miles on any oil with the SAE starburst was the sweet spot. I have been following that logic since then and have had no engine problems what so ever.
Most people think it is cheap insurance. They fail to realize they are wasting oil and driving prices up and supplies down.