I mean, they are intended to preservation, but no one can get hold of them because you have to have the original, so what's the point?.
From what I understand IPF can store non-standard disk formats, something which was possible to do with Amiga floppy drives. So, IPF can be stored exactly as the original, including weird copy protection stuff such as custom disk formatting. ADF on the other hand requires some program modification to get around copy protection.
I don't know how widespread IPF is, but it sure wouldn't be great for Atari 8-bit disks. The way copy protection worked on those in many cases was a physical modification of the disk itself, either by slowing down the drive speed to write "bad" tracks, or sometimes by physically puncturing the media. It may be that the disks you mention above "have to have the original" had something similar done on the Amiga? Because if the disk was modified in some way to have bad tracks I don't know if you could replicate that in IPF, and you would require the original.
