As mentioned before, the line may not be absolutely required nowadays in most countries, but it doesn’t hurt either and makes things more clear (though that doesn’t seem to be the case here).
If the copyright holder of a software wants that his/her software can be used (only) under a specific license, e.g. the GPL or LGPL, the copyrights must necessarily remain at the copyright holder, so that the license can actually be enforced. Otherwise, if the copyright holder decides to give up his rights, the software becomes “public domain” and everybody can do whatever he or she wants with the software - regardless of any software license restrictions!
Nope. That is allowed with the LGPL, but not with the GPL.
If a proprietary ClosedSource application loads a DLL or ShareObject (at runtime) that was released under the LGPL (not GPL), then this is considered a “use of the work”, but not creating a “derivate work”. Thus, the code of the main application can remain under whatever proprietary license it was before, in this case. But with the GPL (not LGPL) it doesn’t matter whether you insert the code as “copy & paste”, link it as a “static” library or load it as a DLL/ShareObject at runtime - in any of these cases you are creating a “derivate work” and thus your own code must be distributed under the GPL too. I’m not a lawyer either, but that’s how the GPL and LGPL are commonly interpreted
BTW: You can still ship a GPL’ed application along with a proprietary CloseSource one, as long as they remain two separate stand-alone programs. And as long as the sources for the GPL’ed application are made available.
Nope. Starting with Version 4.5 the Qt Framework uses a LGPL/Commercial dual license model. The Qt Framework is released under the LGPL and, at the same time, under some proprietary commercial license. The code is exactly the same with both licenses, though the “commercial” license may include access to some bonus tools that I’m not aware of (never used the “commercial” license, because I never needed it).
That is: As long as your application is OpenSource or as long as your ClosedSource application uses an unmodified Qt Framework as DLLs (SharedObjects), you can use Qt under the LGPL. If, however, you wish to link Qt statically into your ClosedSource application or if you modified the Qt Framework (and don’t want to publish your modifications), then you have to buy the commercial license.
At all times, Qt was available under a commercial license that allows developing proprietary applications with no restrictions on licensing. In addition, Qt has been gradually made available under several increasingly free licenses. […] Until version 1.45, source code for Qt was released under the FreeQt license. […] With the release of version 2.0 of the toolkit, the license was changed to the Q Public License (QPL). […] In 2000, Qt/X11 2.2 was released under the GPL v2 […] This was resolved when Trolltech released Qt/Windows 4 under the GPL in June 2005. Qt 4 now supports the same set of platforms in the free software/open source editions as in the proprietary edition, so it is now possible to create GPL-licensed free/open source applications using Qt on all supported platforms. […] On 14 January 2009, Qt version 4.5 added another option, the LGPL. - Wikipedia
BTW: The x264 project uses a very similar dual license model, though they use GPL and commercial, rather than LGPL and commercial.