Apparently if those rolled lips are not vented, you create a massive build up of pressure from heating and whether that be from gas, water, or just air i'm not sure. I would just make sure they have holes drilled in them to be safe. Not to mention a keggle full of boiling wort being tipped on the ground is a sad, sad situation I never want to be in.
By the way...Nice avatar!! A young Jerry and a great photo. I have a NRPS album with photos of Jerry in it when he was in that band and he is really young. Love it!!