That's the difference, plant machinery, etc. isn't built down to a price as much as things like small cars are. The manufacturers can afford to spend the money designing and building a decent transmission because they know that the type of people who'll buy their product *will* care if the transmission is made of tin - they'll have done their research into reliability, etc. before parting with £65K! OTOH, Joe Public doesn't really care or even understand if one car uses a rubber band compared to one which uses a steel one - he does care that car X is £nn cheaper than car Y...
Lets not forget too that car manufacturers don't really care if their cars only last ten years, so building a gearbox that'll last a lifetime doesn't help them at all, especially as Joe Public isn't likely to want to pay any extra for it.
Darren