The other reason: Themes (Score 1)

Don't forget, Harmony is adding the other thing that Qt (and thus, KDE) lacks, real (widget-level) theme support. You can dismiss themes as silly and unneeded, but it is important for these new desktop environments to not only make computing easier, but to make it more fun.

I've heard rumors of QtThemes, (more than just the window border decorations) does anyone know about this?