It's as if the news is a bit of a secret, but, dig into Bing's 5-year anniversary post and you'll see a one-liner.
The Bing Platform puts advanced intelligence in places like Cortana, multi-lingual abilities in Facebook and Twitter, and even powers Siri and Spotlight in the new OSX to help find answers.Bing Powers Apple's Siri and Spotlight In iOS 8 [bing.com]
It's nice that Apple is slowly dropping Google from their ecosystem, it's what Steve would have wanted.
Steve Jobs: "I will spend my last dying breath if I need to, and I will spend every penny of Apple's $40 billion in the bank, to right this wrong, I'm going to destroy Android, because it's a stolen product. I'm willing to go thermonuclear war on this."
More power to Bing. I use them once in a while, I have no problems at all with them getting more market share.