AfxCallWndProc and Custom Control Development

Hi

In Programming with Microsoft Visual C++.NET book, author shows a custom
control dll. In his code:

/////////////////////////////////////////
LRESULT CALLBACK AFX_EXPORT
    RygWndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    AFX_MANAGE_STATE(AfxGetStaticModuleState());

    CWnd* pWnd;

    pWnd = CWnd::FromHandlePermanent(hWnd);
    if (pWnd == NULL) {
        // Assume that client created a CRygWnd window
        pWnd = new CRygWnd();
        pWnd->Attach(hWnd);
    }
    ASSERT(pWnd->m_hWnd == hWnd);
    ASSERT(pWnd == CWnd::FromHandlePermanent(hWnd));
    LRESULT lResult = AfxCallWndProc(pWnd, hWnd, message,
                                     wParam, lParam);
    return lResult;
}
//////////////////////////////////////////

I downloaded The Ultimate Toolbox code, there is no call to AfxCallWndProc
For example:

///////////////////////////////////////////
BOOL COXTabViewContainer::Create(CWnd* pParentWnd, CRect
rect/*=CRect(0,0,0,0)*/,
                                 DWORD dwStyle/*=WS_CHILD|WS_VISIBLE*/,
                                 UINT nID/*=AFX_IDW_PANE_FIRST*/)
{
    ASSERT(pParentWnd != NULL);
    ASSERT(dwStyle & WS_CHILD);
    ASSERT(nID != 0);

    // the Windows scroll bar styles bits turn on the smart scrollbars
    DWORD dwCreateStyle=dwStyle&~(WS_HSCROLL|WS_VSCROLL);
    dwCreateStyle&=~WS_BORDER;

    dwCreateStyle|=WS_CHILD;

    // define our own window class
    WNDCLASS wndClass;
    wndClass.style=CS_DBLCLKS;
    wndClass.lpfnWndProc=AfxWndProc;
    wndClass.cbClsExtra=0;
    wndClass.cbWndExtra=0;
    wndClass.hInstance=AfxGetInstanceHandle();
    wndClass.hIcon=0;
    wndClass.hCursor=::LoadCursor(NULL,IDC_ARROW);
    wndClass.hbrBackground=(HBRUSH)(COLOR_BTNFACE+1);
    wndClass.lpszMenuName=NULL;
    wndClass.lpszClassName=_T("TabViewContainer");

    if(!AfxRegisterClass(&wndClass))
        return FALSE;

    if (!CreateEx(WS_EX_CLIENTEDGE,wndClass.lpszClassName,NULL,
        dwCreateStyle,rect.left,rect.top,rect.Width(),rect.Height(),
        pParentWnd->m_hWnd,(HMENU)(INT_PTR)nID,NULL))
    {
        return FALSE; // create invisible
    }

    // remove WS_EX_CLIENTEDGE style from parent window
    pParentWnd->ModifyStyleEx(WS_EX_CLIENTEDGE, 0, SWP_DRAWFRAME);

    // sign
    ::SetWindowLongPtr(GetSafeHwnd(),GWL_USERDATA,ID_TABVIEWCONTAINER_SIGN);

    SetScrollStyle(0,TRUE);

    CalcLayout();

    return TRUE;
}
///////////////////////////////////////////

In MSJ for AfxCallWndProc:

"You can think of AfxWndProc as a function with a big switch statement that
routes WM_XXX messages to your window class's OnXXX handler functions. This
is a first-order approximation of how AfxWndProc works:

// This is a gross simplification
LRESULT AfxWndProc(HWND hwnd, UINT msg, ...)
{
CWnd* pWnd = CWnd::FromHandle(hwnd);
switch (msg) {
case WM_CREATE:
pWnd->OnCreate(...);
return 0;
case WM_SETFOCUS:
pWnd->OnSetFocus(...);
return 0;
..
..
..
// etc.
}
return 0L;
}"

If AfxWndProc routes WM_XXX messages to window class's OnXXX handler
functions, why didn't Ultimate toolbox use it?
If i derive a class from any MFC wnd class(CWnd, CFrameWnd, CEdit etc...)
haven't it got all the default wndproc for messages(because i derived it from
CWnd class)? So why do we need to call AfxWndProc?