Proving that "true centrists" can't get elected.
Whomever the Republican party nominates in 2012 had best have a plan to recover the estimated 7.5 million voters on the Right who sat on their hands or voted third party. They're not going to replace them out of the moderate middle.
Doesn't prove anything. Quite apart from where he is on the political spectrum, McCain had enormous baggage. Everything from his health and age issues, to his constant betrayal of the Republican Party, to his refusal to take on Obama in any serious way, to his inability to articulate any vision...or articulate anything, for that matter.