As pjc50 notes, it shouldn't; absolutely nothing about creating either ISOs or hard disk images requires root, in theory — it's just a file, after all. But in practice, tools like losetup and mount both require it. The part I found novel in the article was the mtools package, which I didn't know about.
Linux has made progress here, such as FUSE for mounting in user space. But FUSE doesn't support file systems that the OS inherently supports, for example. My understanding is that you need to write a FUSE driver for, e.g., ext2, even though Linux is perfectly capable of mounting ext2 as root.
Block devices and partition tables present another hassle.
I suspect ISOs are more easily done simply because non-root users have more need to create them: UI applications for making ISOs readily exist, but I can't think of any common applications that deal with disk images that don't already have root.
