Also, as the guide mentions, it's possible to mount the partitions with different options. As the following (all mentioned in the HowTo, excerpts from "man mount"):

  noexec Do not allow direct execution of any binaries on the mounted filesystem.  (Until recently it was possible to run binaries  anyway using a command like /lib/ld*.so /mnt/binary. This trick fails since Linux 2.4.25 / 2.6.0.)

  nosuid Do not allow set-user-identifier or set-group-identifier bits to take effect. (This seems safe, but is in fact rather unsafe ifyou have suidperl(1) installed.)

  nodev  Do not interpret character or block special devices on the file system.

Of course this is just one less (perhaps improbable) attack vector. Never the less; many of the mentioned partitions should never have these kind of files unless it's for a malicious purpose.

Edit: fixed pre and clarification