I think nowadays is comes down to a similar thing as boxer's punching vs MMA punching. When you throw a punch in boxing there is nothing you have to worry about aside from straight stand up punching technique. There are no kicks and no take downs.
The same thing with grappling. You don't have to worry about getting hit at all and plus there is the gi to consider. Penn didn't make his mark in nogi grappling, he did it at the mundials (gi). I think that he would be years behind the top gi grapplers today.
We all need some place we can go away to, some place where we can be who we should have been instead of who we are.