Looking at the photo of George and Laura leading the Inaugural Day parade, I got the impression that President Bush honestly is more concerned, and takes more care, about Laura's safety (and their twins') than his own. He knows that they are brought into the public place, and the hot seat that attracts hostility, because of their relationships to him, whereas he chose his course.
I'm sure you're right, Gretchen. The Secret Service is great at what they do, but I'm sure the President still worries.