Google knows exactly what they are doing, making the world safe for Adwords. You only have to look at their annual reports to see that.
They cannot make changes that hurt advertising, they can only make changes that help. By promoting the biggest "information" sites (which aside from Wikipedia are 100% ad dependent), they get the results they want without having to look if they are running Adsense. It's automatic.
Small sites can exist for many reason, many small sites are a person or business that is promoting itself, no ads. They want ads, that's the whole story.