I doubt any of them really would have voted for him, they are just looking for an excuse that doesn't involve them doing any real explaining.
On the idiot scale, Joe Biden is the clear winner, but his 'vast experience' (of being wrong on virtually every issue on which he has taken a position, plagiarism, and being the lapdog of the credit card industry) went wholly unremarked. The media was going to attack the GOP VP pick heartily and relentlessly no matter who it was, since given his hero status it would look too over-the-top to go rabid on McCain himself.