Duty free is only offered on Delta’s long-haul international (not Caribbean) and Asia flights. Alcoholic beverages and headsets are complimentary in all cabins.
Some Delta flight attendants find duty free sales to be an annoyance more than anything else. The commission received by flight attendants for selling duty free items is minimal, and there is fraud in some markets.
The link to the "Onboard Shopping" info section of the Delta website now redirects to their general "In-Flight Services."
Of course all the usual duty-free items will remain available in the sundry boutiques of international airports. And, for those who will truly miss the in-flight shopping experience, there's always the option to route through Asia on Delta's SkyTeam partner, Korean Air, whose Airbus A380s are equipped with an entire mini duty-free shop all their own.