I have worked in maintenance (30 years) for a governmental organization with a large fleet. After long term testing, using oil analysis, it was determined to run all our light duty vehicles on 7500 mile oil change intervals, all using dino oil.
Our police cars regularly turn 200,000+ miles before they are replaced. Modern oils combined with EFI makes all the difference. Engines can be idled for long periods of time without the oil dilution that carbureted engines suffer from. Major engine work or replacement is very uncommon, usually the result of overheating, due to broken hoses or belts and the lack of operator concern.
We tested synthetic oils and they can be run for even longer intervals but the cost difference was determined not to be worth it. We want to inspect the vehicles at least every 7500 miles for other problems.
My 97 Dodge Dakota 5.2 has lived on a diet of Mobil 1 and 10,000 mile change intervals for over 150,000 miles and still uses little oil and the engine still runs the same as it did when new. I just wish the rest of the vehicle had held up as well. YMMV