Comparing the USPS to health care is the most absurd, simplistic idea there is. I'm sick of idiotic naysayers who try to undermine any government program by pointing at the post office.
The postal system is in crisis because there has been a double-digit drop in volume (read: income), but the American Postal Workers Union prevents any layoffs, reduced hours, or wage decreases. When a company is not allowed to make its own decisions to operate profitably in a supply/demand economy—of course there will be huge losses.
I'm all about the freedom to form a union...but sometimes they destroy the jobs they are trying to protect. See also: Detroit.