What we're looking at here is Apple slowly phasing out the last remnants of sales to old devices. It has been impossible for over a year to release new software targeted at people with old devices through the App Store, and it is about to become impossible to sell them new copies of software that was previously released.
This is what gets me about the Apple model (I'm an iPad Mini user -- non-retina) -- the walled garden does an awful lot to preserve the security of the device, but they then brick us old users up in a tiny corner when us and the devices we bought are of no interest to them. If they want to rent us iPads, rent us them. Don't sell them to us then make them useless when the hardware is still working perfectly well.