Keys and change, specifically, won't scratch a modern gorilla glass, although a phone chassis would certainly develop "character." The world is packed full of micro debris plenty hard enough to abrade any glass short of sapphire, and any metal finish short of oil-drilling bits.
Micro-scratching is caused by dust containing oxides of iron, aluminum and silicates. It's everywhere, always has been, but it's worse around (and downwind) of cities and suburbs, because that's what we make buildings and roads and engines and oil-drilling bits out of. It all decays as dust that blows around and clings to you, due to static, water, grease and fiber entanglement.
In a nutshell, the modern world turns people into damp, greasy, walking flap-disks...
and there's nothing you can do about it.
But your phone wants to be like Master Chief...
Don't let it run around a hostile planet without a case and glass covers.
Some device parts can't be protected while remaining usable (e.g., certain buttons, ports, laptop screens, grills for speakers and cooling fans, etc.). However, brazen failure to protect known-fragile equipment, and then generating e-waste if it gets dinged, abraded or micro-scratched... Well, that strikes me as effete, Apple-istically irresponsible behavior.