I'm walking on thin ice here, since I was never in the military, but I don't think McCain's storied service record or the fact that he, unlike Bush, has a child serving in Iraq makes him any more credible on the war. It certainly makes his war support more complicated because he, again, unlike Bush, has paid and may continue to pay a high personal price for America's war mistakes. It'll take more analysis to understand what he gets out of it, where with Bush, it's all just a game. Bush has never had any experience or concept of the human price of war and doesn't see the troops or the Iraqis as human, so he can make a complete mess of things with a clear conscience.
McCain, however, is a little harder to figure out. With all his self-proclaimed "experience" why can't he tell the difference between Sunni and Shia? Why does his handler, Joe Lieberman have to whisper a correction in his ear that Iran is an enemy, not a funder of al-Qaeda? It makes me think that there is a driven compartmentation in the man when facts do not match an ideology ha has invested so much in.
That makes him even scarier than the Bush/Cheney regime we're currently suffering under. Bush and Cheney have never been tested, not like McCain, so their swaggering bluster and eagerness to wield our nation's military as their own personal billy club is easy to see as a yearning for heroism, however misplaced. McCain actually did pay heroism's price, and his son is too. McCain's father and grandfather were both admirals. I only have an observer's perspective on this, but maybe McCain simply cannot conceive of solutions that don't involve military power, either threatened or deployed.
"100 years in Iraq" was not meant by McCain to be flippant. That's one campaign promise he intends to keep.