With a custom install of Florence, selecting X Window System and Gnome also selects kdesupport, kdelibs, and kdelibs-sound. This is unnecessary in a gnome oriented install. These kde packages are selected by the X Window System selection in RedHat/base/comps.
This is intentional - a KDE systems also installs gtk+ and gnome-libs. The reasoning is that most "normal" users will probably want to run some applications from both desktops. If you don't want it, use individual package selection. The X Window System component is our take on what most people (especially non-experienced people; experienced people can always pick individual packages) will probably want. The normal new user doesn't care whether an application is KDE or GNOME as long as it works and is easy to use.