Maybe it's 'cause I don't have a yacht to bring the 360 to or don't have a railroad track running through my house. You know, something that would actually put the system into heavy motion during playback of a disc - which actually is a must for these things to happen.
I'm happy as long as it spins and reads the disc. Had a couple of odd DREs on the one I bought with Dead Rising, so they swapped the drive on it when I had it in for repair because of an RRoD. And... oh... there was some weird bug with DLC in some games 'causing DREs if you played "DLC only" content for a while, allowing the disc to spin down (DRE triggered the moment it needed data from disc again.)