This INode::GetObjectTM() returns the transformation matrix the object needs to be multiplied by to transform it into world space. It is dependent on the context when it is called -- it will either be equal to INode::GetObjectTMAfterWSM() or INode::GetObjectTMBeforeWSM().
The object transformation matrix is not inherited.
ObjectTM = ObjectOffsetTM * NodeWorldTM
ObjectOffsetTM = OffsetScale * OffsetRotation * OffsetPosition