I believe RedHat uses Fedora Core as a 'beta test' release system for their Red Hat Releases.
Sort of the way you would compare SuSE/OpenSuSE to Novell's Enterprise Linux distros. Even tho if you want the same business-class support for SuSE, then you will have to get the $60 version or whatever it is... Then again, Novell's a rather big corporate brand of Linux, anyway. I remember having that distro before switching to Ubuntu for the first time...