Jambone,
The questions are designed to promote a response that reveals something about you as a person. For example you might just as easily have been part of a football team at school, or held a position in a club that involved an aspect of leadership. It isn't a competition based on the role you use as an example, more than a question designed to get you to show what you understand about "leadership" or whatever the topic might be. The same question posed to everybody, will promote an entire spectrum of answers based on each individuals personal experience. The answers should reveal how the individual interprets, reasons, and most importantly communicates a response to the question.
It is important not to be too narrowly focused, but rather look at the broader picture. They are very unlikely to care whether your example was as the head of of a team of advertising executives, or as a member of the school swimming team. It is the way you interpret, reason and respond that they will be more focused on, particularly how that fits in to the rest of the questions and general assesment.