two friends just got ip4 a few months ago. both have cracked screens. one dropped out of a pocket while sitting at the back yard table playing cards, dropped about 20" and shattered. must have been a really lucky hit, you can see the point of impact in the edge. the other let her son play with it (ya, i told her she was a bonehead many times for that), and he dropped it in the kitchen. shattered the front and cracked the back with one hit. the second had a case on it too, sucky.
my droid X has taken a few dips to the ground as well, once to the pavement from my truck and once to concrete from my hand. no scratches, let alone breaks. im pretty happy with that.
its not about "better build" or whatever. if you wrap bacon in glass, eventually you will be snacking on glass shards. putting a case on it helps with that, but hides the aesthetic beauty of the phone itself, which is one of the reasons for buying a phone. i like the way my dX looks, i have no case on it. but mainly due to the pain in the ass that it would be to take the case off every time i got into my truck and wanted to put it in the dock. i do have a screen protector tho, that old habit will probably never die.