Hi,
About ObjectId and 64 bits platforms, from what I read somewhere (I don't remember where) the ObjectId32, OwnerId32 and ObjectIdToObject32 properties and method are only requiered for VBA on 64 bits platforms. By my side I never noticed problems using the 'old' unsuffixed ones with LISP on acad 2010, 2011 and 2012 64 bits (but I do not use as LISP routines as I did).
Another thing, using the "platform" sysvar evaluates the Windows platform version, not the AutoCAD version. On a windows 7 64 bits, I have an AutoCAD 2007 32 bits installed and (getvar 'platform) returns "Microsoft Windows NT Version 6.1 (x64)".
To evaluate the AutoCAD paltform version I'd rather evaluate if ObjectId32 is available :
(defun gc:IsAcad64 ()
(vlax-property-available-p
(vla-get-Blocks (vla-get-ActiveDocument (vlax-get-acad-object)))
'ObjectId32
)
)