I'm not convinced its he best designed, nor is the chap in the first link I posted where he complains that in 9 years of using WPF it hasn't gone anywhere and is pretty complex and bloated to use.
Now a well designed UI is Qt - where they enhanced the existing model with their QML language, so you could create a new control in QML and drop it onto an existing form. All the power of QML whilst maintaining the existing investment in UIs. Qt got it right, shame Microsoft didn't have those devs working for them! (perhaps MS should buy Qt out and use it for new developments, probably too late now they've released Windows 10, but it would have been cool, wouldn't it!)
Imagine if Microsoft had done that instead of reinventing the GUI wheel - you'd create a control in WPF and could drop it onto a Winforms dialog. That would have been good.
As it is, WPF is just now very well designed, and not vey well implemented. As the other link showed, the chart controls only work for small datasets, if you want something that works well - you use the old winforms one! I'd hazard a guess that they are also hardware accelerated purely by being constructed by gdi calls too.
So what's the benefit in WPF? It mignt be easier to construct new controls than winforms but is more difficult to use as an application developer, it performa much worse, and requires a lot more investment in training. If the end result isn;t acceptable to users too.. then its no wonder people are sticking with Winforms.
Or HTML GUIs, which is what I meant by ASP.NET.