I am pretty underwhelmed. Keys are generally made of brass, a soft metal.
If it had scratched the screen I would have been EXTREMELY shocked, because keys have a lower "hardness" than window glass... and I would hope the droid glass is at least of that quality...
The only part of a key that has a chance to scratch glass is maybe one of the "sharper" edges of the keyring, as its the only piece made out of a decently hard metal.
So in fact, the dropping of the keys WAS the best test because that gave the keyring a chance to hit the screen
The real test would be a knife blade(they are typically of equal hardness as window glass) and sand, granite, any kind of pebble that might find its way into your pocket.
DO NOT forgo a screen protector because of this test. Trust me, there are much harder objects than the extremely soft tip of a key in most people's pockets.