What he said.^ Smartglass is available on iOS and Android too. I was hoping they'd give a perk to having a WP though, but it doesn't seem that way. It's still too early to say though.
Another thing Microsoft has to be wary of is promoting it too much. I have a 928 and am all for WP, don't get me wrong. But Xbox isn't just for us. Apple fan-boys use Xbox, feature phone users use Xbox, it's a wide audience. As much as I hate to admit it we don't want to push anyone away. Also, trying to integrate the new Xbox with any Windows platform could be catastrophic. Obviously I'm aware it uses the Windows kernel, but that's not advertising or anything, that's just using what is available to better a product.