This is one reason I don't mind that the only built-in option for search on Windows Phone is Bing. While I believe I get better results from Google (though that may be bias on my part), when I hit the search button it pops up a nice picture. Many times the picture is relevant to a holiday or special event that occurred on that day, and there are call-outs you can press to see quick facts (today's is about Yamuna River pollution and the Taj Mahal).

It's a good example of TheCoreh's point that it's all about providing a more compelling experience. If I was given the option when I first turned on my phone, I likely would have put in Google just out of habit. Today, I probably would not. Probably.