Part of 'winning' is the unexpectedness of the news. Sure, there have been few who said MGS4 would be mutliplat (me included), and we were wrong. However, far fewer people ever said FF13 would be anything but PS3 exclusive. So, given that its going to be exclusive in only one country throughout the whole world is BIG news for MS. That type of surprise is hard to match.
I still think Nintendo will 'win' since MS's only real show stopper was FF13 news. Everything else was meh to nice at best. Only WOW was FF13. Whereas Nintendo hasn't mentioned any games for the last half of this year. There are a couple old ip's that are being strongly rumored to be shown plus you have the new add on to the wiimote for 1:1 controls. All of Nintendo's hardware addons always come with software and that hasn't been shown yet.
Then you have a big black hole in terms of 3rd party software as well. Basically, Nintendo's conference could be huge on new software alone and that would certainly surpass MS's news.
Sony on the other had has really nothing that could complete surprise us. Big price reduction and maybe Home being fully ready and launching tomorrow would be about it.
A motion controller would not be that big, and there are not games they could possibly announce that we haven't already seen quite a bit about.
I guess one other thing, a slim model w/ modest price reduction would be big.