Journals give reporters articles, well in advance of their publication .with the caveat that they cannot release the story until a specified date and time. They defend this practice, saying it allows journalists a chance to thoroughly review complex material, and write better stories. But someone else is presenting a press conference earlier that week, on Tuesday, on the same subject. So they will move the embargo on that one particular paper back to Tuesday, so they can piggyback on the news that's occurring that Tuesday. So clearly, the embargo is just designed to get the journal's name out there in the most prominent position possible.
Reporters usually grin, and bear it.
Otherwise, they risk losing access to the journals and to researchers. But sometimes, reporters break embargoes, deciding that a story is too important, or that the rules have already been unfairly bent. The Seattle Post-Intelligencer's Tom Paulson once broke an embargo on research that linked breast cancer to abortions. The Fred Hutchinson Cancer Research Center had sent out an embargoed press release to local news agencies, including, Paulson says, some outlets that have a policy of not honoring embargoes. He called the center to say he was releasing the story because if he didn't someone else would.