Why don't ATL message handler functions pass the hwnd?

[Bill Stevens]

Is there any particular reason why ATL decided not to pass the hwnd to message handler functions? It seems like that would provide a lot more flexibility. For example, the macro would be like this:

#define MESSAGE_HANDLER_EX(msg, func) \
    if(uMsg == msg) \
    { \
        bHandled = TRUE; \
        lResult = func(hWnd, uMsg, wParam, lParam, bHandled); \
        if(bHandled) \
            return TRUE; \
    }