No, nothing has changed. Qt is still emulatig the L&F as it has always done and is rendering every single pixel of every control itself rather than using the platform native controls. Just look into the source code to see it for yourself.
Ok just for fun I just checked "src/gui/styles/qgtkpainter.cpp" in Qt 4.7.3. It really calls gtk to do the drawing (gdk_pixbuf, gtk_icon, GtkWidget). I haven't checked for the other backends, but wouldn't know why this would be different. You can also check by changing the GTK theme. If it drew fake gtk-ish controls it would ignore that.
Edit, for Vista:
\class QWindowsVistaStyle
\brief The QWindowsVistaStyle class provides a look and feel suitable for applications on Microsoft Windows Vista.
\since 4.3
\ingroup appearance
\warning This style is only available on the Windows Vista platform
because it makes use of Windows Vista's style engine.
Do I need to go on?
And if you can't make it, offer a BTC bounty for someone else to.
+1