Why would it be quite hard to catch or prove? How many fiber optic lines do you think go to Cuba? They could lock down the internet the same way China does. Maybe they haven't gotten around to it yet, but that's not a long term structural argument for the utility of cryptocoins its a temporary moment-in-time argument. Kind of like how at one point a big advantage of buying things on the web was that you didn't have to pay sales tax -- that's not anything inherent in the web, it was just an artifact of governments' lag.