According to Zend Framework Case Study available at https://www.zend.com/topics/Magento-CS.pdf, the Magento project chose to go with industry-standard PHP and the Zend framework because of the extremely simple, object-oriented, and flexible solution that encapsulates best practices and agile testing methodologies and that would result in a very rapid development of enterprise-grade web applications.
Using the Zend framework as the main pillar in the Magento project definitely includes the following advantages:
With the Zend framework, Magento has great flexibility in creating and customizing modules, developing new features for the system, and maintaining the core code.
A basic understanding of Zend components could be interesting for developers to take advantage of this great MVC framework.
You can learn more about Zend framework at http://framework.zend.com/.