I love that quote - by HN's own jrockway - when he was under employ at Google. He wound up effectively retracting and clarifying (2) but I believe it wholeheartedly in original form.
When you take apart Google's "Page Quality Score" algorithm they use to determine what to charge / rank you for each click you can see the brilliant intersection of Google's business and their product.
AKA they believe that the most reliable way to drive search relevancy is to make sure the guy on the other end of the table is willing to pay for that user's attention.
And they'll penalize the advertiser if they don't hit "relevancy" metrics to make it more expensive for that advertiser to reach you.
The relevancy metrics they'll use include page speed (good for user), time user spends on site (relevancy), actions taken - tracked by Google Analytics (relevancy), and content quality / uniqueness (relevancy).
If you've got a guy willing to pay with high relevancy it's a compelling reason to show nothing but ads.
Now is that REALLY good for the user across the board? No way.
Does this leave in the dust the small guys and dramatically favor the big guys with time and attention to get everything right? Totally.
Is every small business going to wind up paying a "Google Tax" - no question.
But still, that's why they do it.
(1) https://news.ycombinator.com/item?id=3535153
(2) http://searchengineland.com/google-clarifies-no-ads-shouldnt...