may not be doable, but the Session selection dialog has KDE/GNOME/default/failsafe/etc and an entry (default selected) called "Last" which IMHO doesn't make sense when the user's just finished a fresh install. IMHO, Last should be disabled (I know, this is per-user, so prob. not a great idea) and whatever the real "Default" is (GNOME in this case, with it and KDE both installed) should get selected (or the "Default" option)
The general problem is twofold; one, you don't know which user is about to log in; and two, you don't necessarily want to read from their home dir, for security reasons. It's possible the whole UI here should be thought through a bit differently, but ideally that would happen upstream - we don't want to change it dramatically in Red Hat packages. So major UI revision suggestions are best filed at http://bugzilla.gnome.org.