Not so sure about this one. Apple and Samsung signed a deal (so many millions of chips at a certain price) until 2014. If it is true then it's because Apple is no longer entitled to volume discounts because they've cut the supply orders. 

http://news.cnet.com/8301-13579_3-57508009-37/apple-reportedly-cuts-order-for-samsung-chips-for-new-iphone/

Since Apple's chip design division has scored a major hit with the A6 line, they could be thinking  now was is a  good time to seek new partners.