bi yearly inspections get more frequent as the car gets older. After your car hits a certain amount of miles you are required to go through an inspection every year. These are quite intense, you have to have your road flare etc etc etc and stuff and its quite expensive to go through inspection. Alot of japanese people think its more cost effective to buy a new car every few years rather than go through inspection.
This is however changing with the hybrid cars as the govt gives more money back to the owners of hybrid cars rather than we get back here.