…many of Medicare’s most significant administrative costs are just covered by other federal agencies, and so don’t appear on Medicare’s particular budget, but are still huge costs of the program. The IRS collects the taxes that fund the program; Social Security collects many of the premiums paid by beneficiaries; HHS pays for a great deal of what you would think of as basic overhead, but doesn’t put it on the Medicare program’s budget.
A look at Table III.B1 on page 51 of the 2012 Trustees report (PDF) shows the amounts Medicare does reimburse the Treasury (IRS), SSA, and HHS for administrative expenses pertaining to Part A. Other tables later in the report do the same for other parts of the program (see comments to this post). I suppose the charge could be that there are still other administrative costs that are provided by one or several of these agencies for which Medicare does not reimburse. If so, I’d l like to know exactly what the Trustees are missing in their report. Right now, my best hypothesis is “nothing.” Solid evidence would be necessary to convince me otherwise.
UPDATE: See comments for pointers to Medicare admin costs for other parts of the program.