The biggest portion of this that kinda of gets me excited is that Zune support was added to the last XNA release. So it seems like MS will try to make Xbox Live the app store for Zune games. It's very doubtful that they even come close to the Apple app store success on the iPhone, but I'm not a Mac developer and I don't care.
They've got to make the Zune appeal somehow, everyone has an Ipod (except me!) so why not tap in to the millions of XBL users and at least try and convert a few