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.
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.