[wpietri]

Google is very unusual as ad-supported businesses go.

Most ads are distractions from content. At Google, because you are actively looking for something, people are much happier to get ads. Especially relevant ones, which Google has invested a zillion dollars in being able to do well. Google also has incredible power to shape the market, so they can get away with forcing ads to be in a form that users like, rather than one that advertisers love.

Google has a further advantage: people generally trust them, even thought they don't know how things work. The general public is much more skeptical of Wikipedia, partly because it's so open.