>Is this entirely correct? What about a proxy/wrapper class in .NET? I understand that sealed classes cannot be inherited. I don't recall seeing the sealed property on any of these classes. IAC, it seems to me that a wrapper/proxy sceanrio could achieve substantively the same thing.

In order to create a COM wrapper class for a .NET Framework base class, you must first subclass and then expose as a COM object. Things like the XMLReader in System.Xml do not allow subclassing, so the only way to do this in .NET would be to create a new class and map all the PEMs via delegation which is not would anyone would want to have to do. Maybe you can try it out and see if you see how this works, or find anything interesting on the topic.