My class with an event:

public class WindowModel
{
    public delegate void WindowChangedHandler(object source, WindowTypeEventArgs e);
    public event WindowChangedHandler WindowChanged;  

    public void GotoWindow(WindowType windowType)
    {
        this.currentWindow = windowType;
        this.WindowChanged.Invoke(this, new WindowTypeEventArgs(windowType));
    }
}

Derived event class:

public class WindowTypeEventArgs : EventArgs
{
    public readonly WindowType windowType;

    public WindowTypeEventArgs(WindowType windowType)
    {
        this.windowType = windowType;
    }
}

Some other class that register it to the event:

private void SetupEvents()
{
   this.WindowModel.WindowChanged += this.ChangeWindow;
}

private void ChangeWindow(object sender, WindowTypeEventArgs e)
{
   //change window
}

What have I gained from following the .Net convention? It would make more sense to have a contract like this

public delegate void WindowChangedHandler(WindowType windowType);
public event WindowChangedHandler WindowChanged;

Doing it this way, I don't need to create a new class and is easier to understand. I am not coding a .Net library. This code is only going to be used in this project. I like conventions but am I right when I say that in this example it does not make sense or have i missunderstood something?