Actually, I find that the top ranked things usually have what I was searching for -- often that's W3Schools or Wikipedia. I'm not a big fan of W3Schools site design, and I wish they had output examples, but, really, the site design isn't bad enough that it makes it unusable as a reference, and usually when I get it at the top of a search results page, I'm usually looking for a quick reference.
Google does not take revenue into account in its ranking, or the decisions on how it changes its ranking. It is neither a signal, nor does it influence which signals are used.
You might be interested in this: http://searchengineland.com/too-many-ads-above-the-fold-now-...
Google demotes pages that have too many ads, including Google's ads.
"It doesn't help to give people a better page if they aren't going to click on it"
I think you've lost me. Don't people tend to click on the top result? And isn't the idea to put the highest quality results at and near the top so people go there? How could it possibly be helpful to the user to not offer them the best quality results?
I looked at the link you provided, but I'm as confused as the author. Isn't there a limit of three Adsense units on a page anyway? As the author points out, Google suggests to publishers that they use the maximum number of ads, and specifically (see the heat map) that they put them above the fold. Then it appears they've decided to penalize publishers who follow this advice. The only way for this to be consistent is if they're only penalizing pages displaying competing advertising products.
The author also shows a screengrab of Google's own results page, where we can see that everything visible on the monitor is sponsored content, with no organic search results at all.
Frankly, I'm perplexed about what point you were trying to make by suggesting this link, but it was interesting.
Almost anyone would agree that the mayoclinic result is higher quality. It's written by professional physicians at a world renowned institution. However, getting the answer to your question requires reading a lot of text. You have to be comfortable with words like "Nonsteroidal anti-inflammatory drugs," which a lot of people aren't. Half of people aren't literate enough to read their prescription drug labels: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1831578/
The answer on yahoo answers is provided by "auntcookie84." I have no idea who she is, whether she's qualified to provide this information, or whether the information is correct. However, I have no trouble whatsoever reading what she wrote, regardless of how literate I am.
That's the balance we have to strike. You could imagine that the most accurate and up to date information would be in the midst of a recent academic paper, but ranking that at 1 wouldn't actually help many people. This is likely what's going on between w3schools and MDN. MDN might be higher quality, better information, but that doesn't necessarily mean it's more useful to everyone.