'The buck stops here'--period.
I think that my reply to Tom, below, sufficiently addresses the first part of your message. It really doesn't matter how the mistake happened, Bush is responsible. Period.
But you said something else that illustrates why Bush's mistake was so egregious:
The more scary possibility is that he slipped the stuff out of the country, perhaps to Syria. If that happened, then we can only hope to find out about it and retrieve the stuff before it falls into the wrong hands.
One of the many rationalizations given for the war was fear that Saddam Hussein would supply WMD to terrorists or other enemies of the United States. If the weapons truly were smuggled out of the country, then Bush's war precipitated the very nightmare scenario he promised to prevent. America could pay a heavy price for Bush's little mistake.
Do you begin to understand why I'm not willing to let you Bush partisans sweep this under the rug?