I'm betting a large part of Microsoft's presentation will be focusing on the new XBox contract plan and Halo 4, and I'm sure they've got some aces up their sleeve. I think they are just being pretty successful at keeping things close to their vest this year, which is why we have no idea what they are going to really show.
But I too think Nintendo's going to get the lion's share of the attention this year because of their next-gen game console with its tablet controller.
I think they'll talk about apps too. I can't see them only talking about these things though. MS and Sony have to have something up their sleeves. MS needs to show some games along with Halo 4 and I'm not sure about Sony. They seem to have blown some of their software reveals pretty early.