1. WinAPI (both 16- and 32bit versions)
5. IE toolkit
6. Office toolkit
7. WMP toolkit (?)
All of those touch WinAPI at some point but they look, feel and behave differently. Java, Delphi and GTK applications also draw their own widgets. No idea about Qt.
Yeah, there's no rhythm or reason to this madness. Qt is the least of their worries.