The U.S. Navy's stance on salvaging wrecks has a lot to do with:
Human Remains
Where human remains are concerned, United States Navy policy has been clear for some time: "salvors should not presume that sunken U. S. warships have been abandoned by the United States. Permission must be granted from the United States to salvage sunken U.S. warships, and as a matter of policy, the United States Government does not grant such permission with respect to ships that contain the remains of deceased servicemen... " (DOS 1986; UNESCO 1994).
This is not a new policy as the Navy's involvement with USS Tecumseh illustrates. Tecumseh was lost in 1864 during the battle of Mobile Bay with 93 men on board. In 1873, Tecumseh was sold for salvage by the Department of the Treasury to James E. Slaughter of Mobile for $50 (West 1995:27). After the purchase, Slaughter let it be known that he intended to use explosives to blast the wreck into salvageable pieces to recover iron and possibly the ship's safe.
In 1876, the relatives of the men lost on Tecumseh petitioned Congress to stop this salvage. Congress quickly passed Joint Resolution No. 23 on August 15, 1876 directing the Secretary of the Treasury to return the $50, with 6% interest to Slaughter and empowered the Secretary of the Navy to assume control and protection of Tecumseh. Congress stipulated that any salvage must provide for the removal and proper burial of the remains of the crew.
Another example from the Civil War, concerns the remains of the crew of USS Tulip. A boiler explosion sent Tulip and most of her crew to the bottom of the Chesapeake Bay. Only a few bodies were recovered, and these were buried on shore within site of the disaster. Correspondence in Navy files dating to at least three periods in 1929, 1951, and 1967 show continued Navy concern over the remains of both the crew members buried ashore and those carried down with the ship (Ellicott 1929; Heffernan 1951; [Eller] 1969). The Navy refused a 1967 request from a diving club for salvage rights to Tulip primarily on the basis of "nondesecration of crew members entombed in sunken naval vessels. " Other considerations were ordnance still on board and damage to the historic and archaeological integrity of the site.
Conclusions
The refusal of permission to the salvage of Tulip shows that as early as 1967 the Navy considered such wrecks to be war graves and of historic significance. The Navy staff involved were from the Naval Historical Center and the Navy JAG, Admiralty Division. The individuals in these Navy branches foresaw the importance of sunken ships and aircraft for interpreting the history of the United States and its Navy.
Today, the Navy recognizes that it has under its jurisdiction some of the most significant historical properties within the United States. Many, if not all of the Navy's sunken warships, are eligible for listing on the National Register of Historic Places, for these are reminders of the actions and events that forged the nation. These sunken vessels and aircraft also represent the courageous actions of those Americans who have earned a permanent place in United States history and are the final resting place for many who sacrificed their lives for their country. Sovereign immune status is a key concept and doctrine for all those who seek to protect a nation's naval heritage, whether U.S. or foreign, from willful destruction and wrongful taking. It is also the raison d'etre for the Navy's policy concerning its ship and aircraft wrecks.
http://www.history.navy.mil/branches/org12-7h.htmThere's more to it than that and if you go to the source you'll see their legal stance on it in it's entirety.
(Whups .... aparently Dan beat me to it while I was composing message - though a slightly different source which doesn't seem to go into as great a detail regarding remains) 
