That might be a reasonable observation in an e-commerce forum, or even in WW's Web-design forum, but AdSense isn't about selling things--it's about running ads for other businesses that sell things.
I'm not sure that the statement is true in any case, because in some businesses, personal service is more important than size. In the travel-agency business, for example, users may like dealing with Expedia and Travelocity for air fares and mainstream vacation packages, but most will prefer dealing with specialist agencies or organizers for things like barge cruises and bike tours. In those specialized categories, bigness may actually work against a vendor. The same thing is true for many tangible products, such as grooming supplies for Bearded Collies or electronics equipment for radio amateurs.
As for why Walmart is putting little stores out of business, that's a topic for an economics forum, not a PPC advertising forum at Webmaster World. :-)