The truth of the matter is that it takes a long time to get an application framework right. It was like that with Winforms, and that contained a few new controls, but a lot of the functionaity was a wrapper around the Win32 API (tell you some thing you did not know already)
WPF will probably reach a satisfactory level of stability and usability in the next couple of versions. after that we will move onto the next big thing. I am currently working with DevExpress controls - not through choice mind - and boy are we coming across some bugs. Each time we update the controls, a few days are lost in the development tracing down bugs, so it really is prefable to tackle projects with something like Winforms, where most of the issues are sorted out, and all the bugs are known with workarounds or avoids.
Basically your argument is that WinForms is better for development right now because it's more mature than WPF. That's a fine argument to make...
...except that WPF has been out since mid-2006, making it over 4 years old now.
WinForms didn't change much in the .NET Framework 2.0 (which, co-incidentally, came out 4 years after 1.0) but was still arguably a very solid UI framework even when it was new. Most of the improvements have been with the designer and the addition of new controls.
So I really don't buy that argument.