Physical examination skills and NNT: number needed to teach

A number of physical examination techniques have been abandoned because of poor reproducibility. Studies have shown that many physicians are unable to use them appropriately. Thus it seems, they simply don't work. Is this type of evidence really applicable to the teaching of physical examination?
Is there any threshold or any NNT (number needed to teach) to justify the emerging practice of omitting the teaching of this techniques?
Why shouldn't we continue to teach these techniques even if there will be only 1 of 1000 students skilled enough to perform them successfully?