QA and dev approach software with different mindsets, and I've noticed in Agile projects where QA is mostly or entirely missing, there is a skill gap.
Edit: People - I'm not trying to be flippant. I really have seen a decrease in quality in the transition to Agile. We use Scrum or Kanban where I work, and while overall the approach to estimation and the smaller scheduling and estimating increment is better, in many projects where I work there is no _separate_ QA group. A few project do retain it (though re-branded as "Performance, Stability, Reliability" - PSR) and it does help, but generally this PSR doesn't cover everything our old QA groups used to cover.
In any case, I have no insight in to what is happening inside Apple. I'm really just suggesting that given the prevalence of Agile methodologies these day, perhaps a non-ideal transition to Agile is a contributing factor to their quality issues.