The point of any academic course is not to provide training (that would be a training course), but to assess the academic level that the students can operate at, in the titles subject domain. In this case the level is Masters, although Iain does not say if it is MA or MSc, and the subject domain happens to be sound design. It is usual at a validation of any course that the course team are asked to demonstrate that there are input and output markets for the course - there is no point validating a course with no input or output. It is usual to look at "demand" for the input and "jobs" for the output, which is probably why this question was raised.
Do sound designers "need" a qualification to get a job? Clearly the answer would be no. There are many avenues that can lead to a career in sound design and as it is practice-based, experience and creativity are always needed. However, if you look at the masters level academic benchmarks: knowledge, understanding, analysis, critique, synthesis, evaluation, communication, etc. then I think you start to get a different answer. (I see all of these benchmarks exhibited every time I look on SSD.) Having a Masters in Sound Design just says "I am capable of operating at the appropriate academic level for this subject domain".
Clearly a freshly graduated student is not just going to walk straight into a sound design role on a feature movie. However, if they were to apply for a junior post the employer would be able to know "This person has some of the academic skills needed.......now lets see what there practical and creative skills are like."
EDIT: I should also point out that I am not saying you cannot gain academic skills without doing a qualification. However, it may offer a speedier path to enlightenment. I often tell my students that having a masters will not mean that they will be able miss rungs on the career ladder, but it may offer a speedier accent once they are on the ladder and may open up other ladders that they had not thought about. However, as discussed by others here, they will require some talent as well if they are to work in sound design.