I found this gem of a statistic recently while reading David Bornstein's How to Change the World:
In 2002, of the twenty largest service-providing nonprofit organizations in the United States (excluding governmental and religious groups), twelve had been established prior to 1920 and seventeen had been established prior to 1960. None was established after 1980. By contrast, more than half of the thirty companies included in the Dow Jones Industrial Average in 2002 were added to the index after 1980 (displacing other companies), and more than a third were added after 1990.
Bornstein uses this to encourage innovation, stating that more good could be done in the world by charities if we had some new blood in the mix, like the corporate world. I tend to agree with him.
But we can't throw out the reality of longevity, either.
The true skill of a leader, then, is to determine which traditions must survive and which ones aren't fit to. This is what really keeps you and your organization around - the ability to know when to build upon the past and when to tear it down and begin again.