There are quite a few people who aren't so tech-savvy that unknowingly use Bing because it's the default in IE. I'm guessing they're the majority of that 27%.
They're also probably the ones that type "google" into the Bing search bar to get to Google. :)
In my experience if you set a search engine other than google to the "not so tech-savvy" they will use it to search for "google" and then proceed from there.