My experience tells me that you need to select the item first to make GetItemData return the correct value.
That is,
code:
for (var i = 0; i <= OptsWnd.Combo_GetCount("CmbStatus"); i++){
OptsWnd.Combo_SetCurSel("CmbStatus",i);
Debug.trace(OptsWnd.Combo_GetItemData("CmbStatus", i));
}