Description:

The /etc/X11/xinit/xinitrc script use the following code to call xinitrc.d scripts:
# start some nice programs
if [ -d /etc/X11/xinit/xinitrc.d ] ; then
for f in /etc/X11/xinit/xinitrc.d/?*.sh ; do
[ -x "$f" ] && . "$f"
done
unset f
fi

As a consequence all scripts that do not use the .sh extension in xinitrc.d won't start when xinit is called. For instance, 30-dbus [dbus 1.8.0-1], pulseaudio [pulseaudio 4.0-6] and 40-libcanberra-gtk-module [libcanberra 0.30-4] are affected.

Additional info:
* xorg-xinit 1.3.3-3

Steps to reproduce:
1/ Start xorg through xinit (ex: using startx)
2/ dbus-launch --sh-syntax --exit-with-session is not started even if /etc/X11/xinit/xinitrc.d/30-dbus has executable privileges
3/ Rename /etc/X11/xinit/xinitrc.d/30-dbus to /etc/X11/xinit/xinitrc.d/30-dbus.sh
4/ dbus-launch --sh-syntax --exit-with-session is started correctly.

This is just an example with dbus, bug the problem is more general. I would suggest changing the xinitrc script from:
for f in /etc/X11/xinit/xinitrc.d/?*.sh ; do
to:
for f in /etc/X11/xinit/xinitrc.d/?* ; do