Why are their wages not being garnished as would those in the private sector?
“Why are their wages not being garnished as would those in the private sector?”
They are. Once the IRS catches up with them. These would have been due April 2008. The wheels of government turn slowly. Their paychecks WILL be garnished for non-payment of taxes (provided they have not resigned).
The reason Government Printing Office and Postal Service are among the highest is that they are by and large blue collar workers and will just get employment elsewhere.