The root file system is the only file system that doesn't need /. and /.. to be special.

The special case is when a file system is mounted as a non-root filesystem, as then /mount/point/.. needs to appear to refer to the same inode as /mount does. The same is true of chroot(). The Linux code seems to jump through quite a few hoops (with functions names like 'graft_tree()') to deal with mounts...