Since Red Hat Enterprise Linux (RHEL) 5 came out in March 2007, it has become quite long-in-the-tooth compared to Ubuntu and other flavors with much faster release cycles. It's of course Red Hat's policy not to upgrade components to ensure the maximum amount of backward compatibility, so this lag is to be expected. Additionally many Red Hat support customers are weary of installing packages from other repositories like EPEL or freshrpms. Thankfully RHEL 5.6 added the ability to run PHP 5.3, but most other components were still missing and out-of-date.