I hope, by "permission" they understand that
the material is now under
the GNU FDL, and that if someone feels like it, they can remove any
attribution or back links.
The GNU FDL requires that the original main authors be acknowledged,
and also that URLs of the original version of the document be
retained. Removing these attributions would be a breach of copyright
law.
But even if it weren't: surely, the more interlinks between open
content projects we have, the better.
Axel