"which requires payment for their hard work."
I beleive that it is important for enterprises to make money. In fact, I beleive that you can make lots of money from open source software - just not by selling it. Pardon me if I am reading anything into your comment.
"If they use Qt then they have probably a comercial lisence from Toll Tech, thus they don't have to give away their source."
That is true. But the skype binaries can (and do) use the GPL qt libraries. Is this prohibited or not?
This is what I mean by having it both ways.
Again, this demonstrates the differences between Gtk and libqt.
Qt is a commercial product which currently has a free licence. Gtk is a Gnu product which has always been free. Of the two, I think that GTK has a better chance of remaining free.