Why doesn ZF support PHP 4?
Zend Framework was built to use all of the advanced object oriented features of PHP 5. Since PHP 4 is not fully forwards compatible with PHP 5, the Zend Framework community was faced with the decision of committing to support PHP 4 or leveraging existing and future enhancements in PHP 5 from the outset. We felt the overall value proposition was tipped in favor of PHP 5 feature, performance, and security enhancements. On top of that, PHP 4 is officially unsupported by the PHP community as of 2008-01-01, and no critical security updates will be published after 2008-08-08.
