Last year, Microsoft became the default search provider for Siri in the iOS7. This year with the release of iOS8 and the OSX Yosemite, Microsoft Bing becomes the default search provider for the new Spotlight feature. During WWDC keynote demo, Apple demoed this feature as well. Microsoft later confirmed the same with the following statement,
Last year Bing became the default web search for Siri, and will now also be the default web search provider in the redesigned Spotlight search feature for the next generation of iOS and OS X. We’re excited about extending the Bing platform to help iOS and Mac customers find what they need to get things done.
Now, Microsoft has to deliver high quality search results to keep Apple platform users from changing the default provider back to Google. Because of the contractual agreements between Apple and Google, Google remains the default search provider in Safari in both OS X and iOS.