When they really need to. But they'll fight it hard! Apple's business model is to lock everything down -- very closed indeed. This does not align with the goals of bitcoin, at least, how I perceive them.
tl;dr Apple = closed. BTC = open.
I think that Apple does not consider Bitcoin as a competitor. Bitcoin is most likely treated as a payment instrument. High volatility in the market makes it difficult to accept bitcoin. If the cryptocurrency market becomes more civilized, then I am sure that Apple will accept payments in Bitcoin as well.