Takes what risks ? Buying the riskless new transistors that TSMC puts out because they know that they work ?
Apple taking risks would be making the chips themselves (see: the failure that was itanium and how it screwed Intel because they had to reorganize their facilities for it), not buying it wholesale and just having TSMC print it.
And if you think that risk is small / nil I would point you to Intel's recent track record.
And just to point out that Apple actually does bear the risk you've highlighted as Itanium was a design (which Apple does) not a manufacturing failure.
You could say the same thing about Intel until they blew it with 10nm. Who knows what the future holds
Also blaming Intel's process problems on Itanium (discontinued 2011) is - well an interesting perspective!
Apple pays the money and takes the risks, so they get the rewards.