rlange - 1:27 pm on Mar 16, 2012 (gmt 0)
So why is there a difference in the CTR? If I had to speculate... Google has more (perhaps better too) advertisers that will be seen on the first page. I bet there isn't a lot due to the ad positions.
According to the summary, the study only measured the click-through rates for organic results.
In this case, i am not certain that the questions are adequately answered
Have you downloaded their whitepaper? I haven't, but it should give more information about their methodology so you can judge for yourself.