Depends on whose use cases you're considering.

There are about 3.6 billion people surfing the web and experiencing PNGs. That use case, consuming PNGs, seems to dwarf the perhaps 100 million (somewhat wild guess) graphic designers, web developers, and photo editing professionals who manipulate images for publishing (in any medium) or archiving.

If, on the other hand, you're considering the use cases envisioned by PNG's creators, or the use cases that interest the people processing or publishing images, yes, these people are focused on format itself and its capabilities.

I suspect this particular use of "use case" isn't terribly clear. Also these two considerations are not incompatible.