Here is the official explanation from the U.S. Department of Defense (as relayed via the National Rifle Association) on why the department suspended sales of expended brass to the civilian market.
".....DLA also put to rest various theories and rumors that were circulated on the internet, concerning the reason for the suspension. As DLA explained to Senators Baucus and Tester, and to NRA-ILA, DoD officials responsible for the de-militarization of military property temporarily halted the release of the cartridge cases last week, pending review of a policy change issued last year by the Office of the Secretary of Defense, which, in the interest of national security, halted the sale of items within a broad category of government property including, but not limited to, surplus small arms cartridge cases.
"To make cartridge cases eligible for sale once again, DoD demilitarization officials verified that the cases could be appropriately placed in a category of government property allowing for their release for use within the United States, and then executed the recategorization. Whereas during the brief suspension, fired cartridge cases would have been releaseable only if the purchaser crushed or smelted them, now the cases may be sold as before, intact and reloadable. DoD also assured NRA-ILA that companies previously authorized to purchase cartridge cases under Trade Security Controls need no further vetting at this time, and are eligible to resume purchasing cases under the policy adopted yesterday."
Riiiiiiiight. A business/national security decision. It still reeks of politics, considering the current state of ammunition supplies in the United States right now, and concerns over crime and potential new gun controls.
Regardless, thanks again to everyone who called their senator or representative to Congress. Also a huge thanks to Sens. Baucus and Tester for their yeoman's work in pounding some snse into D0D officials who thought this was a wise policy, and were clueless about the implications of their decision (which was implemented with no rational explanation, other than that they could do it if they wanted to).
At least now we have an explanation.