Page 9 is very revealing.
Unlike any other public or private entity, under a 2006 law, the U.S. Postal Service must prefund retiree health benefits. We must pay today for benefits that will not be paid out until some future date.
and...
Adopting a traditional “pay-as-you-go” method would produce an average of $5.65 billion in additional cash flow per year through 2016.
In other words....?