Very good guess, you're right. Microsoft's anti-spoofing solution, called "Sender ID" was kicked back by the IETF because of intellectual property issues. As of now, Microsoft refuses to disclose what IP claims it has or patents it intends to file over the solution, and because of the license it couldn't be implemented in most free software, including the server running most of the Web -- Apache. Microsoft wouldn't even agree to disclose everything and accept the standard RAND (Reasonable And Non-Discriminatory) terms.
It other words, it looks like Microsoft wants to own how email is transmitted, and control who can and can't implement the standard.
XML is an open standard in and of itself
And totally useless without a published DTD.
Why shouldn't Microsoft keep that software marketable and not release the APIs for its use?
Fine, but don't claim they support interoperability when they restrict access to their data formats. That's exactly the opposite.