The documentation for QWidget::activateWindow() function says:

On Windows, if you are calling this when the application is not currently the active one then it will not make it the active window. It will change the color of the taskbar entry to indicate that the window has changed in some way. This is because Microsoft do not allow an application to interrupt what the user is currently doing in another application.

The BringWindowToTop() windows api function allows this however, see:

http://msdn2.microsoft.com/en-us/library/ms632673(VS.85).aspx

So activateWindow() could be implemented to allow a window in an application that was not active to become active, or an additional function could be added for this, if it is not feasible to change the behavior of activateWindow() at this point.