I'm a very stiff individual, never been able to touch my toes despite years of trying to stretch. As a consequence, my strokes in tennis are affected and I can't look like pros or copy their technique - my body just doesn't do certain thinga! To me, part of the "natural" way of learning tennis is knowing what your particular body can and can't do. Andy Roddick's serve is aided by his body type - he has an ability to bend like others can't. Trying to copy Roddick would be futile and frustrating, to say the least.
Are there other people with similar limitations? Is trying to teach them cookie-cutter technique a mistake? I don't know the answer, but it's worth considering, imo.