On the face of it, even if true, it was settled business. And it really has nothing to do with Cain's ability to govern.
It has plenty to do with his ability to get elected.
But whatcha gonna do?
And why is that? If true, apparently the woman didn't think this was bad enough to pursue, until now. I can understand the bit about Anita Hill and Clarence Thomas, because, he was going to be actually dealing with laws pertaining to sexual harrassment. And she actually testified.
In any case, "famous" people are subject to this kind of nonsense quite a bit.