That's because few people, even Republicans, really know about Rudy's stance on important national issue. They only drank the media Kool Aid on Giuliani because of 9/11.
I think there is something about him. . . the charisma thing. Not unlike the Kennedys for lack of a better analogy. The standing that a senator like Ted Kennedy has with voters is far out of proportion to the respect that people have for the positions he takes on the issues. This is not to say that I equate Guiliani with Kennedy. I give Rudy a lot more credit than that.
Of course I'd much prefer George Allen as nominee and Rudy as his VP. But if it comes down to Guiliani or McCain, it's going to be the former for me. I'm not worried that Rudy has a screw loose.