I have seen both as well. I think most of the dogs I've seen (I was training in holland in knpv) were working cause they love to work, but they are good at their particular job because they have been taught from an early age (you pick up your prospect at 6 weeks) that making mistakes isn't an option.
I don't know how other dog sports are but in knpv you are training your dog with the help of the club, so the dog is used to being handled by different people from a young age. Usually when he passes his test he is already reserved by the police pending the passed exam.
I don't know if you'