Possible Duplicates:
What does WPF still have to offer over Silverlight 4?
Why change from WPF to Silverlight 4
I'm working on a WPF application. We considered using Silverlight instead of WPF, but decided we want a full blown desktop application with the whole unique desktop application feeling and advantages that gives. However, starting today there has been a lot of buzz out there about Silverlight 4 being announced at PDC09, and people stating that there aren't many arguments left to choose WPF over Silverlight (4).
So; what's the buzz about Silverlight 4? Why can Silverlight now be used instead of WPF? And when should WPF still be used?
The fuzz is that Silverlight 4 will have many of the most commonly used features of WPF that were previously lacking.
The reason Silverlight 4 can be used instead of WPF is it now has the ability to run outside a browser and access the local filesytem.
WPF should still be used when you need features that aren't available in Silverlight 4. See answers to this question for a discussion of which features those are.
I'm only speculating as to why, but I'd imagine that the recent hype behind Silverlight 4 is simply because it's the latest thing to be announced. WPF has had its fair share of updates in .NET 4.0, so I don't think it's going anywhere.
One of the biggest differences between Silverlight and WPF is that Silverlight is sandboxed, so I still see a place for WPF in desktop applications.
来源：https://stackoverflow.com/questions/1758300/why-is-wpf-loosing-terrain-with-silverlight-4-coming