I would tend to agree that this could be part of Apple's reasoning, as well, aside from cost. There must be a reason for the continued use of "traditional" displays over the newer OLED displays. Too costly to manufacture? Too closely to switch manufacturing processes or suppliers? Locked into a contract with an existing supplier? Or just better display overall, but not in every way?
I imagine there are a few reasons. Cost being a great consideration. OLEDs are more expensive to produce. And Apple likes to keep their margins. No doubt, their power management and OS would need to be tweaked when they switch. And so on.