To announce a wedding, promote a product, spark interest in an issue. But manipulation is a very different thing. There is the relatively benign form, say between public relations people and the press. Your client wants publicity, so you cook up some crazy stunt, knowing reporters can't resist telling the story.
Politicians do the same thing, staging rallies of photo ops solely to make the six o'clock news.
The manipulation gets more dangerous when they try to plant misinformation to get their spin on an important issue or event. Journalists must stay alert, pursue the facts, checking their sources to minimize this. Increasingly, there is yet another form of manipulation. In the quest for ratings, a news organization may willingly participate in the spin of the story is big enough. When Barbara Walters or Katie Couric sit down with the Ramseys, they know they are airing a one-sided story.