I just posted more info about this very problem in bug 357346. It looks like upstream xfce4-session did run gnome-keyring-daemon --start and capture/export the environment variables, but an ubuntu-specific patch disabled that behavior in a misguided attempt to fix another problem. The patch is called xubuntu_gnome-keyring-daemon-compat.patch
I just posted more info about this very problem in bug 357346. It looks like upstream xfce4-session did run gnome-keyring- daemon --start and capture/export the environment variables, but an ubuntu-specific patch disabled that behavior in a misguided attempt to fix another problem. The patch is called xubuntu_ gnome-keyring- daemon- compat. patch