Licensing a work using a GPL-ed library under the LGPL
The matrix under
says that a work using a GPL-ed library can be licensed under the LGPL
"if you convert to GPL". For example the KDE libraries which use the
GPL-ed Qt libraries are themselves licensed under the LGPL.
But I don't understand what is the meaning of licensing something under
the LGPL if it is effectively under the GPL anyway because it uses a
GPL-ed library. So what is the point in licensing it under the LGPL?
Could it be that parts of such a work which do not use a GPL-ed library
can be used under the LGPL? Is there such a legal distinction between
"parts that use the GPL-ed library" and "parts that don't"?
A related question is about the people who have contributed code to Qt
under BSD/MIT-style licenses (see
http://doc.trolltech.com/4.3/licenses.html). They have definitely used
Qt's own classes in their own code. I also don't think that all of them
would have got a commercial Qt license which gives them the right to
license their code in whatever way they wish.
In that case, how can their code which uses GPL-ed Qt be licensed under
anything other than the GPL? Is it that the copyright owner of Qt has
granted them special permission to license their code under those free
non-copyleft licenses? If so, isn't it necessary for legal propriety to
mention that in that page?