Amazon renders HTML in an IFrame. If Google does not render IFrames many website's headers and footers won't show.
Regardless this means Google's Web Preview will be producing numerous undesired impressions in Adsense, but they will also be dynamically loading servers like Amazon's.
Frankly I can't understand why there is partial rendering of Adsense ads. It seems like a big bug.
I'm tempted to try implementing NOSCRIPT tags to fill in the ugly white background that shows up wherever there were Adsense ads.