A lot of blogs, because they don't have the time, resources, or inclination to do otherwise, publish rumors -- and fast, to get a jump on competing blogs and on mainstream media.
In an article that points out that problem (published by the New York Times, the pinnacle of MSM), Damon Darlin wrote an illuminating article, "Get the Tech Scuttlebutt! (It Might Even Be True.)"
Darlin cites the rumored acquisition talks between Apple and Twitter, which several blogs ran despite a sense that the talks were not taking place. As TechCrunch's Michael Arrington said, "It was interesting, and it didn't hurt anyone to write it."
That casual attitude towards accuracy, Darlin notes, was a component of early 20th century newspapers, known as "yellow journalism" and typified in "Citizen Kane," "The Front Page" and dozens of early movies whose settings included the newspaper. But newspapers eventually realized they needed to be accurate.
Not the case with blogs.
As Arrington told the Times, "Getting it right is expensive. Getting it first is cheap."
Or, as Brian Lam, who built Gizmodo, said, "The only way to compete with a news organiztion with more resources is to fit between the cracks...If we don't do have rumors, what do we have as journalists?" His answer: "You have press releases," which is how he justifies what they do. "So maybe there is some honor in printing rumors," he told Darlin.
For PR functions, this article and quotes are instructive. These are sites that don't honor embargoes (check out Can PR Embargoes Survive in a Web 2.0 World?) and have already said they prefer to post stories quickly rather than fact check them. I understand that, and it makes sense for them. It just means PR people need to be careful when approaching these blogs.