Really? My iPhone 5 is covered in tiny scratches, and I feel like I've made a real effort to keep it away from keys and change. No major structural damage, just lots of little scratches.
In my experience keys and change don’t matter. The metal is too soft to scratch phone screens. (Besides being soft, keys and change also tends to not have much in the way of really sharp edges. Maybe new keys do, but don’t they get quite smooth over time? The aluminium case is potentially a different story.)
What matters is sand. (For what it’s worth my iPhone has three, four scratches after a year. I’m pretty certain they are all from when I slid my phone around on some surface with a grain of sand between surface and phone – which I usually try to avoid, but oh well. That’s it.)
To be honest, though, for me personally scratches don’t matter. In normal usage they are invisible and while they do annoy me I would rather the phone be more resistant to falling down.
Pocket sand, putting your phone face down on any surface where sand might have been is enough for scratches.
It's all about hardness [1], ordinary iron / metal is quite soft (4 - 5) scale on mohs scale, while gorilla glass is at least a 7. It has nothing to do with how "sharp" an object is, paper will never scratch steel and regular keys will never scratch glass. Someone on XDA [2] made quite a passionate case about this.
