Probably the worst election prognosticators out there are political science professors. It galls the political scientists no end that economists usually construct better election prediction models.
My wife's friend worked for Larry Sabato when she was an undergraduate at UVa. Although he tries to conceal it, she said Sabato is a very partisan Democrat. I think his heart is overruling his head here. Although it might be a bad night for the Republicans, it won't be the wipeout that Sabato is predicting.
I think we can see a glimpse of that in his comments about Santorum.