What law is it though Keg? The same one that prevented you from driving faster than the speed limit to catch your flight on time? If you take off after curfew are you endangering others like the fast diver?
75% of EK pax transit Dubai. So the 15+hr delay at SYD (min crew rest is 12hrs and there are no spare crews there) would have costed a mint. The aircraft being delayed and not used on the next sectors, and missed connections for Pax would have taken days to sort out (problem of having such high load factors and aircraft utilisation). The company would have weighed up all the costs and considered the fine the best option if it asked the crew to depart.
Fines of this magnitude do a good job of enforcing the curfew.
German airports are probably a very good example of how curfews can be administered practically. They consider every exemption request on its merits and consider the company history (they don't want you doing it all the time). The will give concession for weather and some tech issues as they also serve the traveling public. And they have good beer too!
The Don