ColourOfSpring - 9:37 am on Apr 19, 2013 (gmt 0)
All they have to do to increase revenue without manipulating the order of the organic results based on advertising revenue since most visitors don't care if it's an ad or organic as long as they find the answer on the page is put more ads on the top of the page, and based on positional click-thru rate, they will increase revenue.
TOI, Google manipulate the order of the rankings via their endless refining of how the algo works. How they instruct the algorithm is not something you (or I) are privy too. So we can't say for certain either way how Google weigh (or don't weigh) the algorithm in their favour, even if just subtly or slightly just to keep them on a direction they want to move in. We can hazard a guess based on their other actions though.