I am at Denver, Colorado right now attending DrupalCon! The founder of Drupal, Dries Buytaert, gave a keynote speech, where he emphasized that the reason why Drupal was so successful was because of its passionate community.
Its amazing how pure passion can bring 3000+ people to attend DrupalCon from all around the world. Its amazing how hundreds of thousands of people contribute high quality code to the Drupal community for free.
Its not just Drupal! Its WordPress, Joomla, Unix, Android and other such vibrant open source communities where users feel that they own the platform, which makes them do hard work on it since they have a feeling of ownership and responsibility towards it.
Do you know how expensive and rare good programmers are? The skill is valuable and these high quality programmers diligently work towards making their baby better.
Dries is right, its the power of the passion!
It takes time to build, but it scales at a high speed.