A blogger I respect very much, Roger Dooley, recently posted about “The Power of FREE.” His Neuromarketing blog is mostly about the interplay between marketing and psychology. You should read the article for yourself, but the bottom line is that offering something for free is an incredible incentive – even where someone might get just as as good a deal for “almost free.”
Many people measure their success by their search engine ranking for their “target keywords.” I would wager that most people care about their Google ranking over other search engines. Most search engines alter the search results by placing paid advertisers at the top. Google does not sell search engine rankings. I would say this is one of the biggest reasons it’s considered the gold standard of search engines.