Thats because when you ask your average repubican voter who they want for president they only know of Mccain and Rudy and those two tend to split the vote. Ask blog readers and political activists who they want for president(because these people follow politics and are more likely to vote than your average republican voter in a primary) and they rank mccain toward the bottom of the list.
You ask Pro-America who their vote will be with in 2008 and they'll say Senator John McCain.