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.