Ah but you see, a house plant is recognized as a litter box by most cats...LOL...even if there is not quite enough dirt to completely bury the poop. Any one who has had both cats and larger houseplants can relate to that.
I have never seen a cat use someplace where they couldn't at least try to bury it...like concrete.
Again, it depends on the cat - including the cat's age and physical condition.
We have had elderly and ill cats that have not even attempted to find a "good" place to defecate or urinate. When the urge hits, well, that is the place they go.
Whatever the differences in cats and their habits, however, UK_Cat's neighbor apparently has cats that wander into UK_Cat's yard to poop and they do not bury their waste. It is a problem that
could have a legal solution - an injunction, perhaps, and/or an award of damages.
Because animal feces left where children play can lead to health issues for the children, I don't think UK_Cat's concerns are all that unreasonable. That said, my own kids play in areas where there are rabbit and deer and other wild creatures defecating with abandon and it has never led to any noticeable health problems. I worry more about ticks and fleas.