Google makes it’s money from search (duh), so it would make sense that they want to be the default search engine for the iPhone. But, premier placement ain’t free. Google is likely going to pay an estimated $3B for that privilege this year.
“Given that Google payments are nearly all profit for Apple, Google alone may account for 5 percent of Apple’s total operating profits this year and may account for 25 percent of total company OP growth over the last two years.”
Google relies on Iphones for half its mobile search sales, so there is a lot of weight on their relationship with Apple.