Re: the Peacock story. The student has missed some of the particular issues concerning highly specialist medical research. Frequently done with n<20 (due to lack of realistic subjects) and heavily invested in an ethical framework, it is common for medical research in specialist areas to be conducted in the form of case studies. Controls in these cases aren't "people that weren't treated" but "responses prior to treatment" - the student asking the question has a simplistic grasp of the peculiar issues surrounding medical research.

Remember that science is about rigorously reporting what is observed. It is possible to do good science without having to slavishly demand a control group - for example, where is the control group or the null hypothesis in the field of taxonomy?

The student in the anecdote does ask 'why' and I'm all for that, but I would have preferred the anecdote to answer his question rather than just leave it as a joke.