That feature is called Aero Snap in Windows, and occurs if you use Windows API to drag the window around. In our WindowChrome (and RibbonWindow), we do use the Windows API for drags and that's why it works for those.
The dragging of docking windows is a different story though. In our product, we aren't dragging an actual window when you drag the docking windows around. We capture the mouse, show various preview adornments as appropriate, and wait for the mouse button to be released. The window appears after you release the mouse button following a drag, assuming you ended up floating it.
Visual Studio on the other hand immediately creates a real window when you drag, and the window tracks with the mouse. Aero Snap kicks in for their docking windows since Windows API must be handing the drag.
The only way we'd be able to support Aero Snap for docking windows is to completely rearchitect our dragging system to work the way VS does it. I will make a note of the request, but that would be a massive change.