They started migrating several releases before 4.10, maybe that's why.
To sum it up, I'll paste this: "In short, QML makes it very easy to write fluid user interfaces, while retaining speed. The advantages expand well beyond the mobile application sphere, and represent a new way to do GUIs." http://jontheechidna.wordpress.com/2012/05/19/my-thoughts-on...
Aaron Seigo also had some good points on his blog (If I remember well) but I couldn't find them now. Check his blog nevertheless, it's worth it: http://aseigo.blogspot.com/
Qt Quick has many advantages over traditional Qt widgets:
1. It provides a simple JSON-like declarative syntax for defining UI layouts, and is quite easy to write new layouts for different use cases (desktop, tablet, netbook etc)
2. Very easy to do animations
3. Qt Quick is fully OpenGL accelerated in Qt 5 and beyond. While this KDE release is not using Qt 5, it provides a good transition path for the future.
