Tom Evslin has a post about why he thinks one great programmer is wort 50 good ones.  He primarily defends his point with the lack of interfaces creating greater productivity:

If one person can do a whole project,
there is a whole layer of complexity, documented interfaces, and
misunderstandings that is eliminated compared to having two or more
people working on the project. Meetings don’t have to happen; schedules don’t have to be synched; joint-testing and finger pointing over faults doesn’t happen. No personality conflicts, either. The actual amount of work required to do the project is much less when it is being done by one person. Also management time is reduced.
…
But there is more to the productivity gap than just avoiding multiperson projects, as important as that avoidance is. A great programmer, working alone, is usually orders of magnitude faster than a good programmer also working alone.

His point is valid.  However, I think the greatest benefit of a superstar is her inspirational quality.  Can you imagine what it must have been for the rest of the Bulls to play with Jordan?  How can anyone resist being inspired by genius?  Remember Salieri’s awe at his rival Mozart in the film, Amadeus.