How will apps using GNOME's decoration drawing know about my KDE settings, or vice-versa? If I want the close button moved away from other buttons, will I only be able to affect half my applications? Will I need multiple configuration tools?
How will any of these know if I don't want -any- decorations, just a 10px title bar with a title on it?
These "other OSes" you claim are working fine, are so inflexible, and have such insane defaults (which for the most part cannot be changed) that they are nearly unusable to me. This is hardly what I call "working fine". Not to mention the insanity individual apps can, and do, foist on the system..