NavigateBackAction XAML Behavior for Blend

NavigateBackAction.cs

public class NavigateBackAction : DependencyObject, IAction {

    /// <summary>
    /// Navigate the Frame back
    /// </summary>
    /// <param name="sender"></param>
    /// <param name="parameter"></param>
    /// <returns>True if navigated</returns>
    public object Execute(object sender, object parameter) {

        var dependencyObject = sender as DependencyObject;
        var navigate = dependencyObject as INavigate;

        while (dependencyObject != null && navigate == null) {
            navigate = (dependencyObject as INavigate);
            if (navigate == null) {
                dependencyObject = VisualTreeHelper.GetParent(dependencyObject);
            }
        }
        if (navigate == null) {
            return false;
        }
        var frame = navigate as Frame;
        if (frame != null && frame.CanGoBack) {
            frame.GoBack();
            return true;
        }
        return false;
    }

}

Why you search for an INavigate and not the Frame directly? You are casting it anyways