From my understanding iPad vs iPad Air 2
iPad Air 2
Screen: Anti-reflective coating, fully laminated display
size weight: smaller lighter
processor: Better Mutli-Threading, better GPU
iPad
Screen: Brighter
Processor: Better Single Threading
This is a great logistical move for apple, re-using many parts and with the following compromises, allows for the lower price. The iPad Air 2 seems to be the overall better machine. With the iPad Pro in play for upper end performance, this makes sense for a more budget minded build and helps the overall logistics/mass production.
For the iPad Mini, its a little more tricky since its the only one in its form factor, so there was nothing else to change to, however limiting it to only one memory size means one model, makes it cheaper to produce, the savings are also passed on but enable the price/earnings to remain constant, both consumers/device wins.
I would consider these moves as logistical enhancements and savings
passed on to the consumer.
With that said I hope to see new iPads soon! (Pro and Mini)
EDIT: FYI BTW the laminated screen is more difficult/expensive to produce this makes the new iPad cheaper to scale and manufacture. Also the casing size is the same as the pro, so although the inches are re-added, this puts it in line with the size of the 9.7in pro which means thats now on one production front, as opposed to 2 different body versions. This helps offset prices. Economies of scale, could help them also lower the price of the Pros or more likely than not, enable them to put the savings into something better.