Alienware thinks its probably people are banging on the keyboard. Or pressing harder than they should.
The pics I saw showed a couple of very thin pieces of plastic at a stress point. Also, the upper piece appears to be pushed up rather than just broken. I wonder what is under that piece, and if there's adequate clearance from the metal parts underneath and the plastic case.
The problem I see coming is whether this crack is a functional problem or not. It's not likely to be something AW will cover as necessary if it doesn't affect performance. Spending hundreds of dollars a piece to replace a case for an aesthetic issue isn't something anyone does.