Art and press photography are two very different aproches of getting an image taken thats why apart of being photos and trying to express a feeling or situation in a determined way for me it's hard to find any similarities.
And this gives photographers a lot more freedom, to alter and modify almost anything so that a certain aspect, angle, intention is showed.
In this examples by David Lachapelle, its obvious that the pictures have been modified, even specifically design and posed to create a determined message with and artistic degree.Water wave in Japan "Manichi Shibun" Reuters.
Picture of Banana plantation submerged in water in Australia taken by Dave Hunt.
On the press photography pictures should not be altered because the main purpose is to show the truth. The exact moment of an event or action taken place. The job of the photographer is to capture moments, news in the right time, but also in this kind of pictures there is the intention possibility because a specific moment can be capture in many ways, for example in the recent tragic events of Japan, you can see many angles of the destruction, for example a picture of a town completely destroyed, will show the material destruction for a news, but a girl siting and crying in desperation would also show that adding also a more emotional approach.