Of course, there are so many that are frustrated but don't have time to complain to Microsoft or don't know how. Example, my dad was so frustrated with Windows 8 on his new laptop that he asked me to "make it work like it used to". He probably won't be contacting Microsoft himself (though I go an ear full ).
That huge user base also is split over so many versions of Windows so the number would be much smaller for newer versions of Windows. Windows XP is still hovering at around 40% of the Windows market. Those are users that either have decided they don't want to upgrade and face problems they know about (or are content with what they have).