I think there is a very good reason Republicans are going to be hesitant to admit defeat and particularly demoralized when it likely comes: The last time the GOP pitted a grumpy septuagenarian against a charismatic young Democrat, there was never really any hope of winning. Bob Dole never led Bill Clinton during the thick of the 1996 campaign -- though he did in some 1995 polls -- and was frequently down by double digits. After the 1992 Democratic National Convention, Clinton enjoyed a pretty consistent and occasionally formidable lead over George Bush the elder.
Barack Obama has generally had pretty narrow leads over McCain in national polls and, before his spending advantage and the Wall Street mess, had trouble closing the sale in the battleground states. A few national polls show Obama with a less-than-imposing single-digit lead now. Worse, McCain actually led Obama after the Republican National Convention and the Palin pick. There was a point not too long ago where even hardened McCain skeptics like myself thought the Old Maverick might pull it off.
If McCain had been down by 15 points since the Democratic convention, I think a lot more rank-and-file Republicas would be resigned o what's coming. And some of the more conservative of them would be saying, "Screw it, I might as well vote for Barr."