Not holding a paper rating doesn't mean one hasn't been trained. Operators, airlines, certificate holders, agencies...all insist upon and use mechanics trained on their aircraft.
Mr Guppy, How does an A and P Mechanic prove that he/she has had the required training?
An EASA type rating is written proof that an individual has received the approved type training and on job experience (or at least that is what is supposed to happen, in practice I know there are other issues there but that is for another debate).
I don't doubt that good A and P Mechanics are trained but surely there is some sort of proof, that he/she can carry around to wave under the nose of an employer when moving from job to job. I can't imagine the quality department of for example US Airways allowing someone to certify their aircraft without documented evidence of training, experience etc. Which is what a type rating is. No crowing involved it's just very practicle.