Singular Jobs Market

In the wake of this week's hullabaloo surrounding Steve Jobs's health (and let's be serious people, based on every grammar book with which I'm familiar, it's Jobs's, not Jobs') and its impact on Apple, I ask the following questions:

• What makes Jobs different from other CEOs? Company founders? Innovators? Successful culture-builders?
• Does anyone in the world of business - today or historically - compare to Jobs on this front?
• Is Jobs's irreplace-ability, as it were, about the job Jobs does? Or about Jobs himself? Is it good? bad?

What I'm getting at here - at least the thing that interests me - is about exceptional leadership and its transmission over time, about freaks of nature, about sustainability of greatness.