/etc/rc.d/init.d/usb contains following code:

if is_yes "$MOUSE"; then
    action "Loading USB mouse:" /sbin/modprobe usbmouse && /sbin/modprobe mousedev
fi
if is_yes "$KEYBOARD"; then
    action "Loading USB keyboard:" /sbin/modprobe usbkbd && /sbin/modprobe keybdev
fi

This leads to "can't locate module mousedev/keybdev" messages and [FAILED]
status upon startup when using kernel 2.6.x where mousedev and keybdev are
compiled into kernel.
This can be done via /etc/modules.conf:

if -n `kernelversion_minor` < 5
    post-install usbmouse modprobe mousedev
    post-install usbkbd modprobe keybdev
fi