It just looks like the people responsible for marketing the film don't know which actor is which. And they're really bad at guessing. Someone should just take each of them aside and have a word. "Look, Bruce. I know you've got star billing and that means your name has to come first and all that... but because you're the star, we also want you in the middle of the poster and it's making us look a bit, y'know... stupid..."
It's obviously a composite photo - which explains why it appears with the stars in a slightly different order in other versions... like this one...
It may be something to do with the way the poster has been pasted on to the curved wall of a tube station, but the faces look pretty badly photoshopped too.
I mean, those do look like Bruce Willis's features, and it does appear to be his head... but I'm not convinced they're lined up with one another as they are in the real world.
It looks to me as if his features have been dropped in just a little too low and to the left.
Either that or he's had one of those rare Hollywood face-drops people are never going on about.
And as to Catherine Zeta Jones... well, the last time I saw a head meet a neck like that I was playing Cluedo.