Comment by ezzaf

From the article:

"But quartz oscillators have some problems. They don’t keep time as well at high (and low) temperatures, and they’re a relatively large component—1×3 mm or so. In their quest for smaller and smaller hardware, Apple has recently started using MEMS timing oscillators from a specialized company called SiTime to replace quartz components.

Specifically, they’re using the SiT512, 'the world’s smallest, lowest power 32 kHz oscillator.' "

So it was size, not cost that led Apple to be using a susceptible component.