One site has information that could endanger the exclusive going to someone else, so they're threatened in order to have it removed. Other news outlets ignore a story they know is true because it might break their embargo, only to find out that USA Today has the exclusive, so their own stories are going to feel like yesterday's news by the time they're allowed to publish. In some cases, writers go see a game, only to have the details, images, and gameplay details published by the developer before the embargo drops, destroying the value of the pre-release briefing.
via arstechnica.com