My group is currently on its 6th adventure in a Steampunk setting, using D&D's 5th edition rules. With the recent (6 sessions ago) cataclysmic changes in the setting, it does feel like D&D, albeit with a different campaign feel. Here are some of the reasons:
A Year After the Cataclysm
We actually played 5 game sessions using the Basic Rules of D&D 5th edition. All as humans, and none with magic -- though we were told to position as close as possible to the classes we eventually wanted. It was much like Italy set in an archipelago, with strong family ties, internal and international politics, and bits of mystery in a large urban setting (connected by bridges).
There are no gods (they are thought of as fairy tales, and there is no worship, no church to speak of), and there's certainly no magic of any kind (but there are stage and street illusionists and performers). There isn't even a word for it, really.
Then came the Violazione, and the intrusion of magic into the world. Many people died, many people were changed, many islands sank, and life in Piacenza was forever changed.
Adventurers & Regulation
Life in old Piacenza was heavily regulated, and survivors clung to those rules and order even as friends and relatives died and changed before their very eyes. With valuable community resources (and the increasingly undeniable existence of magic) becoming increasingly scarce and unreliable, survivors embraced the need for new regulation -- even if there were occasional squabbles over which groups were prioritized.
Companies of treasure hunters (read: adventurers) would have to have charters in order to operate, and could only take on "official" missions. However, with Piacenza slowly looking outward and discovering new islands where old ones used to be, that may be changing.