Fuel injection and computer controls have come a VERY long way, along with lubricant quality and additives. The oil is lasting longer because there is less unburned fuel contaminating it, due to ignition control, fuel control, combustion chamber design, etc. Also, cars run hotter which gets rid of the water in the crankcase more quickly.
The other thing I've noticed is that most of the "non-car" people (get in, turn the key, and go) change their oil pretty religiously, then trade the car off in 3-5 years, so it doesn't really matter anyway, except to the lucky sap that buys it from them and gets another 150K miles out of it!
Jeff