I'm getting more questions as I start to think about this. They get revenue from ads, not searches. Did they vary the number of ads displayed? Did people look at the first page of 10, not find what they saw, then check the ads, find what they saw (which may be a page two organic result), and click the ad?

If that is what is happening, then I can see why Google would lose. That is, their main conclusion would be that people tend to check organic results first. If that's true then if a company that has to pay to be page 1 is organically moved there by increasing the number of results displayed, then G loses.

They check this by seeing if revenue goes up when they limit the results to 5 ads.

I don't have exact numbers, but well over 99% of searchers never click (and generally won't even look past) the 3rd result.