Now, if you've only heard a little bit about Qt, you might be tempted to think you only need it if you need cross-platform, but in my experience it's actually better than any of the Microsoft frameworks even purely on Windows. (A simple test: write a Hello World program in Winforms, WPF and Qt, then try doing some simple drag operations with the mouse, moving the window around, resizing it. Last I tried, Qt was the only one that updated the window correctly, without flicker. This remained true even after I tried the recommended solutions in Winforms and WPF to reduce flicker.)
The fact that Qt gives you the option of going cross-platform if you ever need it in the future is just a nice bonus.