The problem the USPS is having is not about prefunding pensions and pension plans. Their problem is that they are required to fund future employee health care benefits. No other company in America - public or private - is required to do this.
This is a side note, but... By the way, I am actually a frequent reader of your blog, and I really miss your posts on economics. Link for the curious:
http://crazybear.posterous.com/
Good stuff!