it normal for an iPhone 5 to crack from falling 3 maybe 4 feet

I've had the iPhone 5 for a little over two months now and I use use for class. On Wednesday while I had it on my desk it somehow made its way to the ground, and cracked. I had the iPhone 4 and dropped it at least 50 times before it recieved any clear damage, when i dropped my 5 i was shocked to see that it broke. Is this normal for it to happen to an almost brand new iPhone 5 from a mere 3-4 feet? Not to mention it had a case on it too. And how much does Apple charge to replace this?