Why would they do it? Just look at the buzz that it has generated already, and I think that you can answer your own question pretty easily. With one unsubstantiated allegation, the Yahoos have effectively branded Ohio State as a "dirty" program - that's big time, a journalistic home run! They just manufactured some news, generated some web hits, made some money - even if it turns out to be untrue, so what? There will be plenty more "news" to sell between now and the "credibility hit".
I'd be surprised if the Yahoos did have evidence. Why? Because they didn't present any. And they didn't even say that they had any evidence in their possession, like tapes or emails. I've already addressed the ridiculous three hours to respond argument.
You are right about one thing - journalistic integrity is irrelevant.