I don't (yet) see a contradiction. Opera bought licenses from QT, hence they
can produce closed-source
software. The reason Opera bought license(s) was to keep their own stuff (ie
- the browser) built on top of
QT and other things closely guarded.
The important entity to consider in this entire picture is Trolltech - they
own all copyrights to the code.
So, they have a model wherein they take money from someone (Opera) and give
them the permission
to not release the browser's code.
Trolltech - the copyright owner - has _also_ given the general public which
wishes to use QT under open
licenses the right to do anything with QT as long as they comply with those
terms. GPL v2 and v3 happen
to be two such licenses Trolltech is happy to license under, to such users.
Trolltech - the _owner_ - has the right to choose any license for
distributing their code. _Once_ the code
'leaves their premises' under a certain license (say, GPL) - all further
derivations will need to conform to
that (and compatible) licenses.
So, there's a 'restrictive tree' as you move down - with Trolltech at the
root - as a way of 'visualizing' this.