Windows forms is Honda.
WPF is Orange County Chopper.
It costs more to build a custom hand made chopper, it takes a lot more skill for a worker to do all those components by hand, it requires artistic sense, dedication and allot of work, compared to a worker in a Honda factory that only presses 3 buttons and a bike comes out.
The result?
An Orange County Chopper is unique, beautiful, stands out of the crowd, and makes it's owner prowd, but it is also harder to manufacture, costs more, requires more talent on the builders side and not everyone can do it.
And the point of this rant is?
Use WPF if you want to stand out of the crowd and your clients can afford it ;-)