I see that /etc/gdm/Xsession does run the scripts in /etc/X11/Xession.d/, one of which probably sourced $HOME/.xsessionrc at some time in the past. However, that script currently sources "$USERXSESSIONRC", which is not set by gdm's scripts. (It gets set in /etc/X11/Xession, which never gets run by gdm.) The same situation exists for $HOME/.Xresources .
Confirming on xubuntu karmic.
I see that /etc/gdm/Xsession does run the scripts in /etc/X11/ Xession. d/, one of which probably sourced $HOME/.xsessionrc at some time in the past. However, that script currently sources "$USERXSESSIONRC", which is not set by gdm's scripts. (It gets set in /etc/X11/Xession, which never gets run by gdm.) The same situation exists for $HOME/.Xresources .