While it's true that users can switch between Google, Bing and Yahoo when deciding which search engine to use in Safari on iOS, it's debatable as to whether anyone does actually change it. We're going to put our money on the percentage being on the low side!
That's why being the default search option on iOS is so important. If you're the one chosen out of the box, then the chances are you'll be the one that gets the vast majority of hits from users. Right now, that default choice is Google, and they pay handsomely for the privilege according to Macquarie analyst Ben Schachter.
Just how handsomely, you ask?