Xamarin is working with a great many companies who would think twice about working with Microsoft directly. This way Microsoft can shove money to Xamarin to forward the ecosystem without scaring anyone.
> Oracle and IBM announced in October 2010 that we will collaborate in the OpenJDK Community to develop the leading open-source Java SE implementation, and make the OpenJDK Community the primary location for open-source Java SE development. Oracle and IBM will support the OpenJDK development roadmap that was proposed before JavaOne 2010, which accelerates the availability of Java SE across the open-source community.
I don't think they'd have any issue purchasing Xamarin and importing/re-branding.
Nokia sells to consumers, so there wasn't the problem (as his theory suggests) of corporate clients not wanting to have business with MS.
Not saying that his theory is correct, just that it's different case to Nokia.