How much GNU is there in GNU/Linux?

Yeah, but it's hard to do much without glib these days. It's pretty much ubiquitous. libxml is even more so (though very much in maintenance mode, it makes minimal use of GNOME libraries, and is only really an official part of GNOME because its main developer was a GNOMEr when he started with it, I'd say: it's really a Veillard project.)