You are exactly right. Both emacs and ion have one more feature in common.....complete customizability and transparency. emacs lets you do what you want and lets you do just exactly what you want. The best thing about a window manager like ion is that it is almost as powerful as the X protocol itself.
To say it all in one line.......emacs and ion follow the unix principle. Sorry i would like to add 2 more words...THEY ROCK.