Now you feel the pain of multilib.
Basically the 64-bit install actually installs 32-bit versions of most of the packages so that 32-bit and 64-bit apps will both work.
If you want to use only 64-bit PPC stuff (though I don't know what, if any, functionality will be lost), you should remove all of the '*.ppc' packages. You can do this as root from your favorite terminal: First run "su -" to become the root user (administrator of the machine), then you can use yum's globbing to achieve the removal:
# yum remove '*.ppc'
I highly recommend that you go through the list of removed packages though, just to be sure that no 64-bit (ppc64) packages are slated to be removed.
Afterward, if you only want the ppc64 ones in the future, you can add an exclude line to your /etc/yum.conf
For what it's worth, I've done this to have a "pure" 64-bit install on my Core 2 Duo machine at home (x86-64) and have yet to notice any problems arising therefrom.