Valid point, MJ, however I would hazard a guess that the problem is more prevalent in those instructors with low hours/limited experience who won't necessarily know there is more than one way to teach a given manoeuvre. One of the prerequisites for becoming an examiner is a reasonable amout of experience so I would hope that, by the time people do get that far, they will know that the end result is generally more important than how it is achieved. Unless you are in a tightly controlled instructional environment (e.g. military or Oxford/Jerez etc.) where the method becomes more significant, then how something is done is not important as long as it is safe.
Perhaps FIC instructors are the best placed bods to impart the knowledge that there are different methods for teaching e.g. PFLs, final approach techniques (unless thay already do)?