FWIW, Oil life monitors and manufacturers recommendations are excellent. Contrary to popular belief, there's no fat cat sitting in an office somewhere scraping his oil change profit into a briefcase telling the engineer who designed the engine and the PCM software to increase the oil change interval.
The manufacturers have just as much reason to want to build a quality vehicle with service recommendations that will keep the vehicle running 500K miles as you do. Happy customers are repeat customers. Sure you may drive your car for half a million miles, but the likelihood that you WONT buy another car before you reach that mark is fairly low. Most people have a high mileage 'commuter vehicle' and a weekend vehicle now anyway. If I thought my dodge car was a great car, cost effective to own and maintain, why wouldn't I buy a dodge truck for weekend hauling?
Manufacturers recommendations come from years of research, study, warranty data and repair data. Jiffy lube and dealerships sell oil changes. Remember to consider the source!
As an engineer, an employee of an automotive corporation and manufacturer, and a car guy, I'll say that if you leave your vehicles un-modified, recommendations from the manufacturer will allow your vehicle to last a long time, and not be overly expensive. Most people are unrealistic about the type of driving they do, and the number of short trips they take. You'd be surprised how many people fall under the 'severe duty' schedule of a modern car.