From Fedora Project Wiki
PPC Specifics for Fedora
In order to focus resources in common hardware today, PowerPC is no longer a primary architecture. As a consequence packages are not built for this arch by default and install media is not available for download. Interested PPC users and developers should join the PowerPC Special Interest Group (http://fedoraproject.org/wiki/Architectures/PowerPC) to help make it a succesful secondary architecture.
For a complete description of the differences between a primary architecture and a secondary architecture, refer to http://fedoraproject.org/wiki/Architectures.