Heres what i think,
Japan, Europe and the US all have massive populations compared to us, and they also have a lot of money. This means that even if a small % of the population gets into cars, they have enough market force to support a big after market industry.
Fuel, new car and emissions taxes also play a big part in it too. We have it fairly easy here compared to the other 3 choices. This gives us the freedom to run big capacity engines with much less impact on the purchase and running costs of our cars.
It also has a lot to do with geography. Here in aus, we have a huge country with a fairly spread out population, therefore we tend to spend a lot more time in our cars. This means that many more people take better care of their cars.
We (Aussies) are very lucky to have such a huge local car industry. I think this is purely due to geography. The distance that we have to transport any vehicles that we want to import, adds enough cost to the product to make a local industry viable. Just try and think of another country that has so few people and produces its own cars from the ground up.
I'll have to vote for us Aussies i think. Such a pissant little economy, and yet we can produce world class new cars and have produced some of the legends of motor sport (cars, drivers and tracks). Where else can you buy a family sedan for 40k with over 220 kw. I LOVE THIS PLACE!!