If the vehicle is used solely for short trips, more frequent changes are needed because the moisture that builds up in the oil is never vaporized. You might see some seniors in Florida that just drive from their condo to the supermarket or shopping center in this category, but not a lot of people fall into this category.
The places like Jiffy Lube has valiantly tried to claim that nearly every vehicle is in "severe service" because nearly every vehicle is used for short trips on occasion.
Scientific American got it right:
"According to the automotive website Edmunds.com, the answer depends more on driving patterns than anything else. Those who rarely drive more than 10 miles at a time (which doesn?t get the oil hot enough to boil off moisture condensation) or who start their car frequently when the oil isn?t hot (when most engine wear occurs) should change their oil more often?at least twice a year, even if that?s every 1,000 miles, according to Edmunds. But commuters who drive more than 20 miles a day on mostly flat freeway can go as far as their owner?s manual recommends, if not longer, between changes. As a car ages, more frequent changes might be in order, but that?s for a qualified mechanic to decide on a case-by-case basis.
?The necessity of 3,000 mile oil changes is a myth that has been handed down for decades,? writes Austin Davis, proprietor of the website TrustMyMechanic.com. He says that the economics of the oil change industry demand pushing customers to get their oil changed more frequently?purportedly as ?cheap insurance? against problems cropping up?whether they need it or not. One of the largest oil change chains, Jiffy Lube, for instance, is owned by Pennzoil-Quaker State, and as such has an incentive to sell as much of the company?s traditional petroleum-based oil as possible."
The bottom line is that 3000 mile oil changes are nearly always a complete waste of money. They do not extend the life of the engine one iota. Taking the myth to even greater levels of absurdity, why not change it every 1000 miles or 500 miles. After all it's "cheap insurance" so you should buy as much cheap insurance as you can.