That isn't the only suspect Lincoln quote. There are quite a few of them, as shown by this recent example.

However, the case against him saying the particular phrase mentioned in the articles seems to rely on the fact that it wasn't picked up by reporters at the time. Given the inaccuracy prevelant in the press, I'd hardly consider that conclusive proof. Remember, they didn't have things like tape recorders back then, so they had to transcribe the words as they were spoken. That isn't easy. I don't know if it was common to give out the text of a speech to reporters back then, so that might discount my earlier reservations.

Of course, having a couple people recall something from a speech some 50 years after the fact isn't exactly bulletproof either.