To say you prefer Guiliani over McCain does not mean you would or could ever vote for Guiliani. It's just that McCain pushes people's buttons while Guiliani doesn't. But I can't agree with Guiliani on the issues. So I can't vote for him. McCain is a vain hothead I could never trust. I do not want either of these men for my President.
I see. So, someone who tells a pollster he/she supports Rudy, doesn't really mean that they intend to vote for him. A novel concept. Usually, if one doesn't support either, they register their response as "undecided."