I think one reason people aren't sharpening pitchforks and lighting torches is because every other search engine is one click away. Switching search engines is pretty frictionless compared to switching OSes.
But switching paid search platforms is considerably hairier, especially if you have a large Adwords account with well built out campaigns. There's no way to drive anywhere near the volume of Adwords on Bing, especially once you're running at the margins. So unless you're willing to take a huge hit to business while moving some or all of your ad spending to another engine, there is no real choice to switch.
This is both the beauty and terror of Google's business model. Don't be evil?
According to Alexa, Yahoo! is the #4 site on the internet, and Windows Live is the #7 site. So the millions of people who have Yahoo! and Windows Live for their homepages (and this is very common--remember that IE is still the dominant browser, and it defaults to Windows Live) are aware of those search engines.
The reason Google is the search leader is not because nontechnical people don't know of the alternatives. It's the leader because it's synonymous with search and people think it's the best.
Google is often set as the default search engine for IE in preinstalled OEM configurations (and frequently these days Chrome is the default browser). For antitrust reasons Microsoft can do nothing about this.
