I think a lot of it stems from my dad. He was a engineer of many trades; electrical, mechanical etc. He didn't build model railways for himself, but he did for my brother and then later for me.
Obviously Thomas the Tank Engine didn't help with planting the seeds, but I think it was going to various preserved lines and other shows (car shows, steam fairs).
My other hobbies are playing guitar and working on classic cars, so there is a link with at least two of my hobbies. My day job is an HVAC engineer, so again more mechanical and electrical tinkering.
I think in my case it was nuture. I was always around big, mechanical objects.