COM object types when embedding Excel into GUI

[jnash67]

Can someone please explain these confusing results with regard to COM object types when creating an Excel object for embedding into an AutoIt GUI (as detailed in http://www.autoitscript.com/forum/index.php?showtopic=31963)

When loading an excel object from a file with ObjGet, ObjName returns _Workbook

$oExcelDoc = ObjGet("C:\temp\book1.xls")
MsgBox(0, "$oExcelDoc", ObjName($oExcelDoc))

When creating an excel object with ObjCreate or with _ExcelBookNew (which just uses ObjCreate), ObjName returns _Application

$oExcelDoc = ObjCreate("Excel.Application")
MsgBox(0, "$oExcelDoc", ObjName($oExcelDoc))

$oExcel = _ExcelBookNew(1)
MsgBox(0, "$oExcelDoc", ObjName($oExcelDoc))

When getting the activeworkbook or the activesheet from _Application object, ObjName returns nothing

$oExcelDoc = ObjCreate("Excel.Application")
$oExcelBook = $oExcelDoc.ActiveWorkbook
$oExcelSheet = $oExcelDoc.activesheet
MsgBox(0, "$oExcelBook", ObjName($oExcelBook))
MsgBox(0, "$oExcelSheet", ObjName($oExcelSheet))

When using these objects with GUICtrlCreateObj, only the object that is identified by ObjName as _Workbook works (i.e. doesn't generate a COM error).

How can I obtain a _Workbook object without opening a file? What explains these results?