The store demo units are supposed to lock up, if that didn't happen then someone could stand in front of the unit playing demo indefinitely while other's don't get a chance. I have not heard of consumer models locking up. I tried Maiden 2007 on the 360 demo unit and it crashed too after 4mins.
If you believe that, I've got some prime bridge real estate to sell on ebay. Please use the buy it now option.