Who hasn't ever started writing his own Framework/CMS? It is considered best practice for learning purposes, but going through all the security stuff can be stressful and boring at the same time. That's where most devs start to contribute to big Open Source-projects like Typo3 or the Zend Framework, because they are already experienced working with it and yet evolving another system on the market or even getting people to contribute seems like an unachievable task.
They talk about the evangelizing that all of the Zend Framework tutorial posts do to further the cause of ZF use and how they can help introduce beginners to the framework even easier than them trying to submit bugfixes right from the start. They also talk about the process of contributing back to the Zend Framework - signing a CLA, reading the standards, grabbing the code from the subversion server and checking out the bug tracker for things to get in and fix (and write unit tests for, of course).