Well, he sure has been saying it a lot, and not just at town meetings.
But it is legitimate to tie it to him for 2 reasons:
One, it's a fantasy to think we can stay there without casualties
Two, it effectively illustrates his pervasive flip flopping. He was agin it, 'afore he was fer it.
Let's look at number one. McCain's defense for his 100 years statement is that he wants them there if we don't take casualties, or "our most precious resource" as he called American lives.
If any candidate for national office thinks the Middle East and Europe and Northeast Asia are similar, they need a new foreign policy adviser. Clearly, Germany and Japan were and are highly organized nation states and Korea was a less volatile and very cohesive nation, far more than Iraq. Occupation turned into garrison due to far more dangerous enemies on their different borders. Even then garrison was/is not always welcomed. Our mere presence is a much greater provocation internally in Iraq and externally to the rest of the Muslim and Arab worlds than any garrisons in Germany, Japan or RoK ever was.
After nearly 30 years of engaging directly with the Middle East, if anyone in government thinks uninvited US forces in any Middle east country, or even invited forces in some instances, do not provoke terrorist acts, they need to be posted on the corner of a a very busy Baghdad or Beirut or Damascus market and give a survey. If we station people in Iraq, however many, they will be targets.
So, given that, what will happen when things DON'T settle down under a McCain presidency? Will we leave? Not bloody likely. When does McCain say we should stand down if the situation continues to be violent? The juking he does on this would make a Zoot Suit dancer envious. So if things settle down we stay, and if things don't we stay til they do, at which point we stay. And the Media let's him get away with this circular reasoning. So, his statement is valid to attack because it is circular, and/or naive, and is an out and out fantasy. It will indeed cost further American lives and treasure, and further weaken the nation if acted upon.
On the Second point, the man is a flip flopper extrordinaire. Asked point blank by Matthews about the Germany/Japan/Korea analogy, he rejected it. Now he embraces it. Why? Because he entered the presidential race as a Republican Candidate and had to drink the corporate kool-aid. So, his statement is valid to attack because it shows his transformation from pseudo-maverick to mainstream George Bush Republican, and his willingness to trade truth for power.
His statement was unthinking, dangerous, and unworkable. But then again, that is just what we have had from the Republicans for the past 8 years.