You've never done any GEM programming, have you? When you use the GEM desktop, you're using almost all of GEM's capabilities. It's really quite remarkable how little is there, and it isn't at all surprising that the few successful GEM-based applications (notably the early versions of Ventura Publisher) came with their own extended versions of GEM.

The world is actually better off with Windows as a dominant GUI than it would have been with GEM. It would be better yet had it been X11, but you can't have everything.