I answered WPF on Twitter. You asked why. Since it wouldn't fit in a tweet, I'll answer you here. The answer is less simple than twitter allows.
Either way you have a programmer technology that your trying to fit into an admin world. Both options are a poor fit.
For me WPF is the more declarative less coding way to express a GUI. It is more powerful. It can be less ugly. Show-UI makes that easier.
But,
Since the target audience are not programmers, the tools are horrible. I don't need to repeat your blog here. Some will be able to make them work, others have neither the time nor the inclination.
So the longer, no twitter answer is that most admins probably want to be able to easily do the following:
1. Ask yes/no.
2. Ask a fill in blank question.
3. Multiple choice.
4. Show results that will not fit in a simple OK dialog.
5. Probably a few other things I am not remembering right now.
For all of these WinForms is way harder without a commercial tool. WPF is easier with free tools, but not easy, though Show-UI helps a lot. WPF also presents a ramp that some can climb if they want to create some very powerful UIs. You would hit the wall with WinForms much sooner.
The real answer? Where can I download a function that does what I want cause its past 7 pm and I need to get this done so I can go home. Oh yeah, powershell.com.