Cool. Since I don't own an XBox and can't imagine buying a phone that might blue-screen in the middle of a call, I won't have to worry about ever upgrading to W8.
Over 1/2 of all game consoles are XBox machines (an installed base of about 70 million). There are about 114 million households in the US.
Their primary owners/users are young adults* (the exact same market base that is more likely to use a smart phone).
When these people go to purchase their next smart phone, will the sales pitch “this will interface seamlessly with your XBox” appeal to them? For a lot of them it will.
The fact that YOU don’t own one, doesn’t mean it still isn’t going to be an advantage for MS.