Just noted a Politico post on the Obama cabinet meeting, mocking the idea that DHS can save money by buying office supplies in bulk. The following is pure speculation:
Long ago, when I was a new Federal employee, it was explained to me that the General Services Administration essentially had a monopoly on government procurements. I believe it was a FEDSTRIP program, operated using 80 column IBM punch cards. 80 characters was enough to identify the supply item from the GSA catalog, the quantity, and the destination. For some items, GSA had supply contracts the agency had to order from (like typewriters, etc.).
Over the years the GSA monopoly eroded. A major contributor was Vice President Gore, who pushed for the "reengineering of government procurement", much of it by giving government credit cards to employees who could then go to the local Office Depot store to shop for supplies.
So, DHS may be in the process of reinventing the wheel again, deciding it's cheaper to do centralized purchases than decentralized.
(BTW, for what it's worth, which is nothing, it's possible all the changes were rational. If you compare an existing process, encumbered by lots of junk inherited from the past, to a new process, rationally designed, the new may always win. Of course, rational designs often don't allow for human weaknesses, like fraud, or irrational purchases.)