[Mathnerd314]

Skin is the same everywhere, it seems disingenuous to claim that one skin area needs different care from another without more evidence. Similarly cast-iron pans seems to be an internet thing, soap and/or powerwashing would presumably work just fine.

The only exception I can think of to soap and water for cleaning is delicate fabrics or sensitive optics, but there the issue is the liquid used rather than the general process.

[AstralStorm]

That's not quite true, anal region is slightly more sensitive. There are improved cleaning agents that are less irritating, but are still not commonly used. (Some old bidets have too strong water jet. It's unpleasant.)

It's not as sensitive as mouth though. We don't use soap with grit and fluoride anymore to clean teeth and mouth nowadays.