I have added this to the FAQ:
Q: If the DFSG are to be applied to documents as well as to programs, why is
the text of the GPL included in Debian, if it says that it cannot be
modified at all?
A: It is included because this text contains the terms under which many
components of a Debian system are distributed. Debian is legally required,
then, to inform of these terms to the receiver of the components ? the only
way is including the text in the Debian system itself.
Take into account, however, that:
1. According to the FSF (copyright holder on the text of the GPL) you're
actually allowed to modify the text of the GPL and create a derivative
work if you remove the preamble and you do not call the results
"General Public License" (reference:
http://www.fsf.org/licensing/licenses/gpl-faq.html#ModifyGPL)
2. Actually, if no works in Debian were covered under the GPL, Debian
would not distribute the text of the GPL by itself.
--
Jacobo Tarrío | http://jacobo.tarrio.org/