It's not so much the lighting that I find odd (I can imagine they had so many spotlights that there would be some strange effects), but the sharp silhouettes, even when people stand so close you should have problems distinguishing where one starts and the other ends. Plus: Tom Cruise is 5'7'', Cameron Diaz is 5'9'' without heels. They're next to each other, so shouldn't the difference be more obvious?
As whisky already said, my guess is they took a gazillion pics, chose the ones where each individual looked the least dorky, and then 'shopped them together. IMO, there's no way you can get 116 decent faces and postures at the same exact second, not even with actors.
One would think people at Paramount would be better at 'shopping than this, though.