Well, regardless of the situation, if this is rigged or not, this still shows a very good thing: Microsoft stepping up, pushing for standards support in their browser, and pushing that engine into anything they produce with a real effort.
WP7 shipped with a weird hybrid IE7/8 engine that put bluntly, is one of the worst parts of the phone. This update includes the IE9 engine, which has been a huge step in the right direction on the desktop.
At the end of the day, the fact that this engine is now in the same class as WebKit/Gecko is a boon for the web and web developers. HTML5 apps that I can develop and target iOS/Android/WP(IE9) with? Yes please.