It is also important to have DC as calm and quiet as possible today. So if postal workers in Dubuque get to stay home, it may be because State Dept and Congressional employees, etc in DC would just complicate the works.
OR it may just be a simple honor to an ex-Federal Employee, albeit one from the top of the pay scale.
Understand one of the D.C. airports is closed for this ceremony as to prevent the noise from disturbing the honor.