To continue my "nonsensical rambling", if you keep machine learning in mind and "rolled an update" it's entirely possible "junk" would float to the top to be "weeded out" by the "learning system", but if you were doing it purposely to increase earnings, there's no reason to revert or make the results better over time.
And there's Absolutely No Reason to show a 'big brand' in the top 10.
In reality, what you would do, if your organic results were based on earnings, is to show the little, tiny, obscure sites that can't afford AdWords, because then the "big boys" would have to "pay to play" and the "middle of the road" sites would drive the prices up on them and overall you would make more money.
It would be very easy to justify doing things this way by simply saying "Users seem to indicate finding the 'deep web' and results not provided by 'main stream brands' are better results than 'big brands'... We could be incorrect, but as of now, we present the obscure results rather than 'big brands' because we think those are what our users are looking for in the organic results."
Really, the preceding is an "off the top of my head example" in a few minutes of time, so if I had a week or two to think about it, I'm sure I could word and justify showing sites that couldn't afford advertising in the organic results over anything else, and if they were really manipulating the organic results to make more money, then not showing the big brands is the way to do it.
Showing 'big brands' more often or in higher positions defeats the purpose of making more money, because 'big brands' have deep enough pockets to pay and pay often, where "mom and pop" don't really make anyone any money, because their pockets aren't deep enough to drive the prices of ads way up, so those (mom & pop) are actually the results you'd show to "extract an extra buck" from the SERPs if that's what you were doing with organic rankings.