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