Where is this true?

  It was most likely "sudo rm -rf .*" which will actually go BACKWARDS up the tree as well.

Edit: At the very least, this doesn't work on OS X 10.5, Ubuntu 10.04 (server edition), and CentOS 5.8. For example:

  $ mkdir -p foo/bar
  $ cd foo/bar
  $ rm -rf ..
  rm: "." and ".." may not be removed