That assumes that during regular work, you'd be under stress. If it were the military, then yes, i would agree - working while you're being shot at means you need to be able to work under stress.

However, a lot of people don't do well under stress, and in many corporate settings, there's usually no real source of stress (except perhaps artificial stress induced by management). Someone might work much better in a stress free environment than someone else under a stressful environment, but you'd then easily miss these candidates by structuring the interview to be stressful.