vroot support gone in debian kernel 2.6.18 ... why?

# grep -i vroot /boot/config*-vserver*
/boot/config-2.6.16-2-vserver-686:CONFIG_BLK_DEV_VROOT=y
/boot/config-2.6.17-2-vserver-686:CONFIG_BLK_DEV_VROOT=y
/boot/config-2.6.18-3-vserver-686:# CONFIG_BLK_DEV_VROOT is not set
/boot/config-2.6.18-4-vserver-686:# CONFIG_BLK_DEV_VROOT is not set

Does anybody know, why it's not compiled in since 2.6.18 anymore?