Rolling without time limits is SPORT. How long do you think you'll be able to roll on the ground with someone in a real fight? Someone is going to either put the boot to your head or else you'll submit the guy in a few seconds. Rules, or the lack thereof are only one part of the difference. BJJ is not reality based fighting. Niether is boxing (as Muhamed Ali admitted when he said he'd get his ass kicked in a street fight).