I agree with that. I disagree with the notion that Kerry lost the 3rd debate simply because of the Cheney daughter remark. Kerry looked weak and pale in the 3rd debate. He had no energy and said a lot of goofy things that made no sense.
In the 1st debate, people weren't paying attention to what he said. They were looking for him to be "Presidential". That is, someone they could see as president. He walked like a president and sounded like a president. Once you get past that, his message is gobbledygook.
The problem with singling out the Cheney gaffe is that there have been so many other gaffes since then. Kerry's "ask me about my wife, I'll tell you about my mother" strategery didn't pan out. Also, Edwards' "Vote For Me and The Dead Will Walk" eulogy is something out of a creepy horror film.