It's normal for an LCD panel to be fragile. I'm not sure why the screen would crack, but if it's being pushed past the swivel's limitations, then instead of turning the swivel, you're essentially twisting the television.

If it's as you describe, it would likely not be covered under warranty, but the service department would be the one to give a definitive answer. I'm not an authority on the service matters.

I'm sorry to hear that this happened.