I haven't played My Summer Car myself, but what I've seen it captures the spirit of Finnish countryside backyard garage custom-car scene. I'd guess it comes a lot from similar background as you describe; kids growing up in farms, getting involved in maintaining and fixing the farm machines and learning by doing.

When I was a kid, my parents never did things like that, we didn't have a workshop at home, and I wasn't keen enough to go learn on my own. But that real world 'My Summer Car'-scene is still alive and kicking, a lot of people weld and fix and keep their old cars going. I think that in Finland on average we have older cars on the road than in most of the European countries, and that is because of the widespread DIY-scene. Even people like me who can't weld and fix themselves, they always know someone who does. So I always consult my neighbour who is specialized in re-modelling old VW Beetles; some of his projects look more like building the entire car from a scratch =)