'Whitepapers, official statistics, general averages, and case studies which do not include your site should be used as guidelines and not absolute truths'.
When looking at items like the above, they are often averages. Averages mean some had a higher, and yet others a lower, response to the stat being measured.
I always think it's worth testing something to see if it applies to your particular ad/website.
Using other people's case studies can give you ideas as to what to test; however, I think you're doing yourself a disservice if you take them as law without making sure that it also applies to you.
So, for the initial question, I've had some ads to better with quotes than normal, and others do worse. It depends on the context of the ad itself and not just using the quotes to try and stand out (which could also be a reason for ad disapproval).