Fascinating. It's held at the same time every year. Even if someone asked him straight after the last one to commit to something he'd be able to turn it down. So there's no way he's mixed up two appointments. Also its a four day event. What has he agreed to that is going to last four days? Couldn't he show up a day late or even two days late. Or leave a day early. How odd that this unavoidable clash means he has to miss the whole event which has been at the same every year.

Also note he says he "plans" to give a speech at the Munich Security Conference. Why more details to follow? Why not just tweet a follow up saying he'll be giving a speech. Seems like thats what he hopes he'll be doing but he doesn't know if he'll be able. So he can only say more details at a later date.