I think that's the point. They're trying to capture a market far larger than people who care about the next Halo, because those people are going to buy this anyway.
But they're the people who will be reading the vapid-to-us articles written by those who have no understanding of, or context for, gaming and will simply try to encapsulate what they see on that stage.
If Microsoft gave a 'core gamer only' conference as its reveal, the (e.g.) CNN article the next day would read very differently. And the mother with two children and a kinect would decide, in a paragraph or maybe two, that this next one is not really 'for' her.
And that may well be what core gamers want the message to be. But it is desperately not what Microsoft wants the message to be.
True but the press/blogs will summarize this and a ton of people will have heard about it by the end of the day. They really want to be the only box in your living room, not just something you boot up when you want to play Halo, so they're emphasizing things other than the games at this point.
