Please do not confuse sales with exposure.
Websites have potential for sales. People can either make great livings off of a website or not. Just because sales and profits off of a site are good does not mean everyone knows about it. The loyal and any customer who has dealt with that particular site is knowledgeable about it. Maybe even the target audience knows the site more than the average. And the stats presented probably did not take into mind that they had to use another medium to let people know that their site exists. (ads for a .com site on television, magazine, word of mouth)
With all things in consideration all research is FLAWED in some way. Error happens. Misinterpretation, bias, lack of respondents willing to participate, not representative of the population/target market, and calculation error can happen to any exercise. Anyone can play with statistics results and interpret them differently. Stats are to ideas for companies/people to aid or use in their decisions, not full-hearted beliefs.
There was no indication that I fully believe in those results. Again as a person we all have our own bias. There are some stats that I am curious of how the research was conducted and how they conducted it.
... then again this topic was on something presented by google ad sense, not research agencies/companies.